SEARCH

SEARCH BY CITATION

Keywords:

  • pleomorphic liposarcoma;
  • clinical outcome;
  • tissue microarray;
  • molecular biomarkers;
  • p53 mutations

Abstract

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES

BACKGROUND:

Pleomorphic liposarcoma (PLS) is a rare high-grade sarcoma that has lipoblastic differentiation. In this study, the authors evaluated PLS natural history, patient outcomes, and commonly deregulated protein biomarkers.

METHODS:

Medical records from patients (n = 155) who had PLS from 1993 to 2010 were reviewed. Univariate and multivariate analyses were conducted to identify independent prognosticators. A PLS tissue microarray (TMA) (n = 56 patient specimens) was constructed for immunohistochemical analysis of molecular markers, and p53 gene sequencing (exons 5-9) was conducted.

RESULTS:

The average patient age was 57 years, and the patients presented with primary disease (n = 102), recurrent disease (n = 16), and metastatic disease (n = 37). Lower extremity was the most common disease site (40%), and the average tumor size was 11 cm. Complete follow-up data were available for 83 patients, and their median follow-up was 22.6 months. The 5-year disease-specific survival rate was 53%; and recurrent disease, unresectability, and microscopic positive margins were identified as predictors of a poor prognosis. Systemic relapse (the strongest poor prognostic determinant) developed in 35% of patients with localized PLS. Immunohistochemical analysis revealed increased expression of peroxisome proliferator-activated receptor gamma (an adipogenic marker), B-cell leukemia 2 and survivin (survival factors), vascular endothelial growth factor (an angiogenic factor), matrix metalloproteinase 2, and other biomarkers. Frequent loss of retinoblastoma protein expression and high p53 mutation rates (approximately 60%) were observed.

CONCLUSIONS:

PLS is an aggressive, metastasizing sarcoma. Identifying ubiquitous molecular events underlying PLS progression is crucial for progress in patient management and outcomes. Cancer 2011;. © 2011 American Cancer Society.

Pleomorphic liposarcoma (PLS) is a rare high grade pleomorphic sarcoma; the presence of lipoblasts is required for diagnosis.1, 2 Because of their rarity (less than 5% of all liposarcomas) knowledge of PLS natural history stems from anecdotal reports and small cohort analyses typically contained within larger liposarcoma studies; only 3 PLS-specific reports include more than 50 patients.3-5 Such caveats notwithstanding, these studies demonstrate that, as compared with other liposarcoma histological subtypes (well differentiated/dedifferentiated liposarcoma [WDLPS/DDLPS] and myxoid/round cell liposarcoma [MRC]), PLS is the most aggressive---exhibiting avidity for systemic spread and a poor overall outcome.3-5 Surgical resection is currently the only potentially curative approach to these remarkably chemoresistant tumors; locally advanced and metastatic disease is generally noncurable. This dismal outcome of patients with PLS mandates the development of improved (perhaps molecularly based) therapeutic strategies.

PLS characteristically harbors diverse chromosomal rearrangements and genomic profiles without unifying molecular alterations, a circumstance typical of soft tissue sarcomas (STSs) with complex karyotypes (eg, leiomyosarcoma, angiosarcoma, and myxofibrosarcoma).6-9 In contrast, WDLPS/DDLPS and MRC commonly exhibit distinctive genetic aberrations (ie, 12q13-15 chromosomal amplification in WDLPS/DDLPS and a [12;16] translocation resulting in a fused in sarcoma-DNA-damage-inducible transcript 3 [FUS-DDIT3] fusion gene in MRC).10-12 This genetic complexity suggests that singular, dominant molecular aberrations are unlikely to underlie PLS tumorigenesis and progression. Consequently, it may be more relevant therapeutically to elucidate the currently unknown spectrum of PLS deregulated pathways and/or processes rather than search for a possibly dominant yet nonexistent locus of PLS “oncogenic addiction.” In light of these knowledge gaps, we chose to investigate the natural history and clinical outcome of a large PLS cohort treated at a single institution, seeking to identify disease-specific survival (DSS) prognosticators and to identify commonly deregulated molecular processes/biomarkers using human PLS specimens assembled in a tissue microarray (TMA).

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES

Clinical Database

This study was conducted with institutional review board approval from The University of Texas MD Anderson Cancer Center (UTMDACC). Patients with PLS who attended the UTMDACC from January 1993 through January 2010 were identified by searching the UTMDACC prospective sarcoma database, institutional tumor registry, and pathology archives. Only patients who had unequivocal PLS histology confirmed by a UTMDACC sarcoma pathologist (A.J.L.) were included in the study (n = 155); the presence of lipoblasts was mandatory for diagnosis; and patients who had “pleomorphic liposarcoma” in the background of well differentiated or dedifferentiated liposarcoma or inconclusive diagnoses were excluded. An initial database was constructed that included demographic and tumor-associated variables. For patients who had sufficient follow-up information (n = 83), treatment and outcome information was included. Only patients with localized PLS were included in the univariate and multivariate analyses.

TMA Construction

After an evaluation of all potential formalin-fixed, paraffin-embedded (FFPE) PLS samples that were available, 56 blocks representing tumors derived from 37 patients were selected for inclusion in the TMA. Five FFPE blocks from tumors with each histology—dedifferentiated liposarcoma (DDLPS), myxoid liposarcoma (MLPS), and unclassified pleomorphic sarcoma/malignant fibrous histiocytoma (UPS/MFH)—were included as controls. The TMA was constructed as described previously.13 In brief hematoxylin and eosin (H&E)-stained sections were reviewed from each tumor block by an institutional sarcoma pathologist (A.J.L.) to define areas of homogeneous, viable tumor. By using an automated TMA apparatus (ATA-27; Beecher Instruments, Inc., Sun Prairie, Wis), 0.6-mm punch samples (2 per patient) were obtained from each donor block and formatted into a recipient block. Sections (4 μm) were cut and verified by H&E staining.

Immunohistochemistry

Commercially available antibodies against peroxisome proliferator-activated receptor gamma (PPARγ) (Cell Signaling, Danvers, Mass), adipophilin (Fitzgerald, Acton, Mass), B-cell lymphoma 2 (BCL2) (Biogenex, Fremont, Calif), survivin (Abcam, Cambridge, Mass), p16 (CINtec, Heidelberg, Germany), retinoblastoma (Rb) (BD Pharmingen, San Diego, Calif), cyclin D1 (Labvision, Freemont, Calif), cyclin-dependent kinase 4 (CDK4) (Invitrogen, Carlsbad, Calif), vascular endothelial growth factor (VEGF) (Santa Cruz Biotechnology, Santa Cruz, Calif), matrix metalloproteinase 2 (MMP2) (Millipore, Billerica, Mass), MMP9 (Millipore), β-catenin (BD Biosciences, San Jose, Calif), epidermal growth factor receptor (EGFR) (Zymed, Carlsbad, Calif), mouse double-minute 2 (MDM2) (EMD, Gibbstown, NJ), and p53 (Dako, Carpenteria, Calif) were used for immunohistochemical staining. Spots representing 40 different samples from 37 different patients were applicable for scoring analysis; in 3 samples, both a localized lesion and a metastatic lesion from the same patients were evaluated. Labeling intensity was scored by 2 observers (M.P.G. and A.J.L.) as none, low, or medium-to-high; when pertinent, cytoplasmic and/or nuclear staining were scored separately.

p53 Sequencing

Genomic DNA was extracted from paraffin-embedded tissues using a QIAamp DNA Mini Kit (Qiagen Sciences, Valencia, Calif) according to the manufacturer's instructions. The integrity and concentration of the extracted DNA were assessed with the NanoDrop-1000 Spectrophotometer (NanoDrop-Products, Wilmington, Del). DNA sequencing was conducted as described previously.14

In brief: primers were designed for intron sequences flanking exons 5 through 9 of the p53 gene; primers were purchased from Sigma-Genosys Technologies Inc. (Woodlands, Tex). One hundred nanograms of genomic DNA were used as a template for polymerase chain reaction (PCR) amplification of exonic sequences. PCR reactions were carried out on an Eppendorf Mastercycler Pro thermal cycler (Eppendorf AG, Hamburg, Germany). PCR product sequencing was conducted on an Applied Biosystems 373 automated DNA sequencer (Applied Biosystems, Foster City, Calif). Sequence analysis was performed using Sequence Scanner version 1.0 (Applied Biosystems).

Statistical Analysis

Statistical analysis was conducted as described previously.15 Patient demographics, clinical characteristics, and molecular marker expression levels were summarized using means, medians, or proportions, as applicable. Median overall survival (OS) and disease specific-survival (DSS) were determined using the Kaplan-Meier method. The 1-year and 5-year DSS rates (95% confidence interval [CI]) were calculated for all evaluable patients. For the OS analysis, death was counted as an event. For the DSS analysis, only death from disease was counted as an event, and patients who survived or died from other causes were censored at their last follow-up date or the date they died from other causes. A Cox proportional hazards regression model was used to test the statistical significance of candidate prognostic factors for DSS in a univariate manner. From this model, the hazard ratios for potential prognostic factors were estimated with a 95% CI. Then, all potential prognostic factors with P values < .10 were included in a saturated model, and backwards elimination was used to remove factors from the model based on the likelihood-ratio test in the multiple regression analysis. Fisher exact tests and chi-square tests were used to assess associations between molecular markers. All computations were carried out using the SAS statistical software package (SAS Institute, Cary, NC).

RESULTS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES

PLS Patient, Tumor, and Treatment Variables

In total, 155 patients with PLS were evaluated at UTMDACC during the investigated interval (1993-2010). Only patients who had follow-up available (n = 83) are described in this report. Clinicopathologic variables are summarized in Table 1. The median age at presentation was 53 years (range, 14-84 years), and there was a slight predominance of men. Most patients (80%) presented with localized PLS (primary or recurrent); and 20% had metastatic disease, most commonly to the lungs (82%), liver (18%), and skeleton (18%). The most common sites of primary PLS were thigh (34%) and pelvis (15%). The average size of localized primary tumors was approximately 11 cm. The average size of truncal tumors was 8.5 ± 4.0 cm (range, 1.5-16.5 cm), and the average size of extremity tumors was 11.2 ± 7.2 cm (range, 0.7-30 cm).

Table 1. Patient and Tumor Variables in Patients With Pleomorphic Liposarcoma
VariableNo. of Patients With Follow-Up (%), n=83
  • Abbreviations: SD, standard deviation.

  • a

    Metastatic sites included the lungs in 14 patients, the liver in 3 patients, skeletal sites in 3 patients, and other sites in 1 patient; 4 patients had multiple metastatic sites.

  • b

    Tumor size was available for 53 patients, and only primary lesions were considered.

  • c

    Tumor location refers to the location of the primary tumor only; extremities include upper arms (5%) and lower arms (3%), shoulder girdle (7%), lower legs (6%) and upper leg and buttocks (34%); central includes head and neck (4%), thorax (14%), abdomen (12%), and pelvis (15%).

  • d

    Tumor location was not available for 2 patients.

Age: Median±SD [range], y53.4±16.8 [14-84]
Women/men32/51: Ratio, 1:1.6
Tumor status at presentation 
 Primary60 (73)
 Recurrent6 (7)
 Metastatica17 (20)
Tumor size: Average±SD [range], cmb11.1±7.25 [0.7-30]
Tumor sitecd 
 Extremity49 (59)
 Central34 (41)

All patients with metastatic PLS (n = 17) received chemotherapy (doxorubicin [n = 12], ifosfamide [n = 12], gemcitabine [n = 7], and docetaxel [n = 7]). In the majority of patients (n = 14), extensive and diffuse metastatic load was present, precluding surgical metastasectomy (only 3 patients underwent such surgery). Only 6 patients underwent palliative surgery and/or received radiotherapy.

Surgery was considered for all patients with localized (primary or recurrent) disease (n = 66). Only 2 tumors (3%) were deemed unresectable after radiation and chemotherapy. Complete macroscopic resection was achieved in 62 of 64 patients with localized disease (97%), and negative microscopic margins (R0 resection) were attained in 56 patients (90%) who underwent complete resection. The average tumor size in patients who underwent R0 resection was 9.7 ± 6.3 cm (range, 1.5-29 cm) versus 11.7 ± 6.8 cm (range, 4.5-25 cm) in patients who underwent R1/R2 resection. R0 resection was achieved in 19 patients (79%) who had truncal tumors compared with 37 patients (93%) who had extremity PLS. Chemotherapy (neoadjuvant and/or adjuvant) was received by 28 patients (45%) who underwent complete resection, and the agents received included doxorubicin (n = 24; 89%), ifosfamide (n = 19; 70%), docetaxel (n = 5; 19%), gemcitabine (n = 5; 19%), cyclophosphamide (n = 2; 7%), and dacarbazine (n = 2; 7%). Radiation was delivered to 43 patients (69%) who underwent complete resection, including 25 patients who received neoadjuvant radiotherapy, 17 patients who received postoperative adjuvant radiotherapy, and 1 who patient received both preoperative and postoperative radiotherapy.

PLS-Specific Survival and Potential Outcome-Related Prognosticators

The median follow-up of patients who presented with metastasis was 8.5 months (range, 2.5-47.2 months) (Table 2). The median OS of patients with metastasis was 9.1 months, the 1-year DSS rate was 45%, and none reached 5 years. The outcomes of patients with metastatic PLS were markedly worse than those for patients with localized tumors (P < .0001) (Fig. 1A). The median follow-up of patients with localized PLS was 31.5 months (range, 1.5-182 months). For patients with localized PLS who remained alive at the end of the study (n = 36), the median follow-up was 47 months (range, 2-182 months). Sixteen of the patients with completely resected tumors had local recurrences (25%), and 23 patients (35%) developed metastatic disease, mainly pulmonary spread. Within the constraints of a relatively short follow-up, the 1-year and 5-year DSS rates for patients with localized PLS were 93% and 65%, respectively. Kaplan-Meier analysis further demonstrated that positive microscopic margins were correlated significantly with decreased DSS (P = .001) (Fig. 1B). Tumor size (<5 cm) and disease status (primary vs recurrent) did not achieve statistical significance (P = .07 and P = .06, respectively) (Fig. 1C,D), possibly because of the small number of evaluable patients in the cohort.

Table 2. Treatment and Outcome Variables in Patients With Pleomorphic Liposarcoma
 No. of Patients (%)
VariablePatients With Localized Disease, n=66Patients With Metastatic Disease, n=17
  • Abbreviations: CI, confidence interval; DSS, disease-specific survival; HR, hazard ratio; OS, overall survival; NA, not applicable.

  • a

    Patients with metastatic disease either underwent palliative surgery or received palliative radiotherapy.

  • b

    Refers to patients who underwent complete resection (n=62).

  • c

    Percentages refer to those who underwent complete resection and received chemotherapy (n=27) or radiotherapy (n=42).

  • d

    The median follow-up for the entire cohort of 83 patients was 24.7 months.

  • e

    Refers only to patients who underwent complete resection (n=62).

  • f

    Refers to all patients who had with localized disease at presentation (n=66).

  • g

    Several patients had multiple sites of metastases; percentages refer to the group with metastatic disease only (23 patients).

  • h

    The 5-year DSS rate for the entire group was 53%.

  • i

    The 1-year DSS rate for patients with metastasis was 45%.

Treatment variables  
 Surgery: Yes/no64/2 (97)6/11 (55)a
 Type of resection  
  Complete surgery62 (97)3 (18)
  R056 (90) 
  R16 (10) 
  R2: Incomplete2 (3) 
 Chemotherapy28 (45)b17 (100)
  Neoadjuvantc18 (67) 
  Adjuvantc11 (41) 
 Radiotherapyb43 (69)3 (18)a
  Neoadjuvantc25 (60) 
  Adjuvantc18 (43) 
Outcome variables  
 Follow-up: Median [range], mod31.5 [1.5-182.3]8.5 [2.5-47.2]
 Local recurrencee16 (26)NA
 Metastasisf23 (35) 
 Site of metastasisg  
  Lungs/thorax16 (70)NA
  Liver2 (9) 
  Abdomen5 (22)NA
  Skeleton5 (22) 
 5-Year DSS: HR/95% CIh0.65/0.52-0.78NAi
 Median OS [range], y7.28 [2.9-14.7]0.76 [0.53-1.58]
thumbnail image

Figure 1. These Kaplan-Meier curves illustrate pleomorphic liposarcoma (PLS)-specific survival stratified (A) according to patients who were treated for localized disease (solid line) versus metastatic disease (dotted line), (B) according to R0 resection (solid line) versus R1 resection (dotted line), (C) according to tumors <5 cm (solid line) versus tumors ≥5 cm, and (D) according to primary disease (solid line) versus recurrent disease (dotted line) at presentation.

Download figure to PowerPoint

A univariate DSS analysis was performed to identify factors that predicted a poor prognosis in patients with localized PLS (Table 3). No surgical resection, microscopically positive surgical margins, and the receipt of chemotherapy were associated significantly with decreased DSS. Large tumor size and recurrent disease at presentation to UTMDACC did not achieve statistical significance, possibly because of the small number of evaluable patients in the cohort. These variables (except chemotherapy) were included in a multivariate analysis; and recurrent disease, no surgical resection, and positive resection margins were identified as independent poor prognostic indicators. It is noteworthy that our analyses were limited by the relatively small patient numbers, and combining datasets from different institutions may enhance the statistical significance of clinical information.

Table 3. Univariate and Multivariate Cox Proportional Hazard Models for Disease-Specific Survival in Patients With Pleomorphic Liposarcoma
VariableHR (95% CI)P
  1. Abbreviations: CI, confidence interval; HR, hazard ratio.

Univariate analysis  
 Tumor size: ≥5 cm vs <5 cm3.6 (0.83-15.64).09
 Tumor status: Recurrent vs primary3.04 (0.88-10.49).08
 Surgery: Yes vs no0.07 (0.01-0.38).002
 Surgical margins: R1 vs R03.96 (1.42-11.02).008
 Chemotherapy: Yes vs no2.94 (1.2-7.24).02
Multivariate analysis  
 Tumor status: Recurrent vs primary5.05 (1.38-18.51).01
 Surgery: Yes vs no0.04 (0.001-0.23).0003
 Surgical margins: R1 vs R05.87 (1.99-17.29).001

PLS-Related Molecular Biomarkers

Little is known about PLS-associated molecular deregulations, and such knowledge may enhance disease diagnosis, prognostication, and treatment. Therefore, we evaluated protein expression of multiple cancer-related biomarkers using immunohistochemical analysis of PLS patient specimens assembled in a clinically annotated TMA that included all 3 PLS subtypes: classic (n = 28), myxoid (n = 6), and epithelioid (n = 6) (Fig. 2). Marker selection was based on previous reports suggesting their potential relevance to PLS or malignant neoplasms per se, including markers of adipogenic differentiation (PPARγ, adipophilin), cell survival (BCL2, survivin), cell cycle regulation (p16, Rb, cyclin D1, CDK4), angiogenesis (VEGF), migration and invasion (MMP2, MMP9), and also β-catenin, EGFR, and p53. The majority of stainings were conducted at the clinical laboratory using highly validated antibodies; and, in all experiments, positive and negative controls were used to confirm antibody specificity. Table 4 and Figure 2 depict protein expression levels for the entire PLS cohort as well as representative photomicrographs of stained specimens; as reflected in the heat map, for each antibody evaluated, a spectrum from no staining up to high staining intensity could be identified across the TMA specimens.

thumbnail image

Figure 2. Protein biomarker expression is illustrated in samples of human pleomorphic liposarcoma (PLS). (A) This heat map summarizes expression levels of each protein that was evaluated in individual scorable samples (note that vascular endothelial growth factor [VEGF] was scored only as positive or negative). UPS indicates unclassified pleomorphic sarcoma; DDLPS, dedifferentiated liposarcoma; MLS, myxoid liposarcoma; PPARγ, peroxisome proliferator-activated receptor gamma; BCL2, B-cell lymphoma 2; Rb, retinoblastoma; CDK4, cyclin-dependent kinase 4; MMP, matrix metalloproteinase; EGFR, epidermal growth factor receptor; MDM2, mouse double-minute 2; MMP, matrix metalloproteinase. (B) These images demonstrate representative levels of immunohistochemically evaluated markers in human PLS specimens (insets show control sections: PPARγ, low expressing PLS; adipophilin, DDLPS; BCL2, low expressing PLS; survivin, low expressing UPS/malignant fibrous histiocytoma [MFH]; p16, low expressing PLS; Rb, high expressing PLS; CDK4, DDLPS; VEGF, negative expressing PLS; MMP2 and MMP9, negative expressing PLS; EGFR, low expressing PLS; MDM2, DDLPS; p53, low expressing PLS; original magnification, ×200).

Download figure to PowerPoint

Table 4. Pleomorphic Liposarcoma Biomarker Expression Analysis
  Biomarker Expression Level, %
MarkerPositive Staining: No. (%)aLowModerate/ High
  • BCL2, B-cell lymphoma 2; CDK4, cyclin-dependent kinase 4; EGFR, epidermal growth factor receptor; MDM2, mouse double-minute 2; MMP, matrix metalloproteinase; PPARγ, peroxisome proliferator-activated receptor gamma; Rb, retinoblastoma; VEGF, vascular endothelial growth factor.

  • a

    The total number of scorable specimens for each marker varied because of different rates of sample attrition.

  • b

    VEGF staining was scored as positive versus negative staining only.

PPARγ nuclear39 (100)2377
Adipophillin32 (80)1000
BCL237 (93)7327
Survivin   
 Cytoplasmic39 (100)4654
 Nuclear39 (100)973
p16 Nuclear40 (100)3070
Rb9 (23)6733
Cyclin D113 (33)1000
CDK412 (30)4258
VEGFb27 (68)
MMP237 (93)4951
MMP939 (100)4456
β-Catenin27 (68)4159
EGFR28 (70)5050
MDM20 (0)00
p5322 (55)4159

It is noteworthy that PPARγ was expressed in all PLS samples as well as in DDLPS, myxoid liposarcoma (MLS), and UPS/MFH control specimens; and 77% of PLS samples exhibited moderate-to-high PPARγ expression. Adipophilin expression was observed in 80% of PLS specimens, albeit mainly at low levels. In controls, only MLS exhibited adipophilin positivity. Both BCL2 and survivin were expressed commonly in PLS (93% and 100% of specimens, respectively). Moderate-to-high survivin expression was identified in 54% of PLS specimens, and both cytoplasmic and nuclear staining were noted. In addition, p16 was expressed in all PLS specimens, and 70% exhibited moderate-to-high staining intensity. In contrast, 77% of PLS specimens did not express Rb. Cyclin D1 was expressed in 33% of PLS specimens; in contrast, all DDLPS specimens expressed this protein. Similarly, CDK4 expression was observed in 33% of PLS specimens, and all DDLPS samples expressed various levels of CDK4 protein. VEGF expression was observed in 68% of PLS specimens. MMP2 and MMP9 were expressed in 93% and 100% of PLS specimens, respectively, and moderate-to-high expression was noted in >50% of PLS specimens. Sixty-eight percent of PLS specimens expressed various levels of β-catenin, although the expression was mainly cytoplasmic. Enhanced EGFR expression was noted at either at moderate-to-high levels (35%) or low levels (35%).

Recently, it was reported that a high rate of p53 mutations was observed in PLS.16 To further evaluate p53 mutational status, we sequenced the p53 DNA core binding domains (exons 5-9) in DNA extracted from 31 FFPE PLS specimens. In that analysis, p53 mutations were identified in 19 samples (60%) and included mutations in exon 5 (arginine [R] to proline [P] at codon 158 [R158P], arginine to valine [V] at codon 159 [A159V], and arginine to histidine [H] at codon 175 [R175H]), exon 6 (H193R and arginine to threonine [T] at codon 209 [R209T]), exon 7 (serine [S] to tyrosine [Y] at codon 241 [S241Y], glycine [G] to alanine [A] at codon 245 [G245A], and arginine to glutamine [Q] at codon 248 [R248Q]), exon 8 (leucine [L] to proline at codon 265 [L265P] and threonine to isoleucine [I] at codon 304 [T304I]), and exon 9 (S313T). Of these, S313T, L265P, and R248Q were the most frequent (Fig. 3). We considered the possibility that this high mutation rate may have been a false-positive artifact caused by the sequencing in formalin-fixed tissues; therefore, we blindly sequenced 2 samples for which corresponding frozen samples were available, and identical p53 sequence alterations were identified. No statistical correlation between p53 mutation status and p53 protein expression levels could be identified (Fig. 3).

thumbnail image

Figure 3. These are representative sequence chromatograms of the 3 most commonly occurring p53 mutations in samples of pleomorphic liposarcoma (PLS) and tabulation of p53 mutational status and protein expression levels in individual PLS samples. A indicates adenine; C, cytosine; T, thymine; G, guanine; WT, wild type; L, liposarcoma samples; M, myxoid liposarcoma samples.

Download figure to PowerPoint

Next, we evaluated whether biomarker expression levels were correlated with the outcomes of patients with PLS. This analysis included only samples from patients with localized disease who underwent complete surgical resection and for whom follow-up information was available (n = 22). Univariate analysis failed to identify prognostic value for any markers evaluated, and the caveats inherent to small sample cohorts rendered definitive conclusions problematic. Future attempts will be made to increase the number of samples retrieved from patients with PLS who undergo complete resection to enable meaningful evaluation of the prognostic value of a given biomarker.

DISCUSSION

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES

The current study and other major series3-5, 17-20 demonstrate that patients with PLS have unfavorable outcomes even when managed with multidisciplinary expertise at tertiary cancer centers, reflecting the aggressive biology of this malignancy. PLS exhibits high rates of local recurrence, as indicated in previous reports.3-5, 19, 20 In our series, 25% of patients who underwent complete surgical resection experienced local failure. Systemic (especially pulmonary) metastases were common; 25% of our patients presented with metastatic spread, and >33% who underwent complete resection developed distant metastasis during follow-up. This aggressive tumor behavior was exemplified further by 5-year survival rates of approximately 60% for patients who presented with localized disease (Table 5). Multivariate analysis identified recurrent disease and positive microscopic margins as independent prognosticators of outcome in this series. Other clinicopathologic factors that were identified previously as potentially predictive included older age, central tumor location, tumor size >10 cm, tumor necrosis, a high mitotic rate, and epithelioid morphology (Table 5).3-5, 19, 20 A gene expression signature capable of predicting outcome in patients with complex karyotype STS recently was devised,21 and the validity of that profile should be tested in a cohort of patients with PLS. If it is validated, then PLS genetic profiling possibly may augment traditional staging, thereby optimizing patient treatment decisions.

Table 5. Summary of Published Pleomorphic Liposarcoma Clinical Series
ReferencePatients With FU5-Year OS, %5-Year DSS, %Disease Prognosticators
  • Abbreviations: DSS, disease-specific survival; FU, follow-up; NA; not available; OS, overall survival.

  • a

    DSS of patients with primary disease/recurrent disease.

  • b

    Status refers to tumor status at presentation (primary vs recurrent localized disease).

  • c

    Including 66 patients with localized disease and 17 patients with metastatic disease at presentation.

  • d

    DSS of all evaluable patients.

  • e

    DSS of patients with localized disease.

Downes 200119184550NA
Gebhard 200234857NAAge, location, size, margins
Homick 200445063NALocation, size, necrosis, mitotic rate, epithelioid subtype
Fiore 20072060NA81/64aSize, statusb
Dalal 2006564NA59Age, sex, status, location, marginsb
Current study83c4953/65deMargins, statusb

Unraveling the key deregulations that drive PLS inception and progression is essential to establishing molecular-based staging systems, as suggested above; and even more critical is the potential impact such knowledge may have on the development of novel and effective anti-PLS-targeted therapeutics. The elucidation of specific PLS nodes of vulnerability awaits a determination of the molecular underpinnings of this malignancy: Common “drugable” targets are yet to be discovered. The cytogenetic complexity of PLS suggests the probability of multiple molecular aberrations rather than single “oncogenic addictions.” Strategies to disable multiple parallel and/or complementary pathways, rather than single-locus “magic bullets,” likely are necessary for the effective management of PLS, hence our efforts to identify biomarkers that broadly reflect different cancer-associated, therapeutically relevant processes.

Tumor suppressor pathway deregulations commonly occur in PLS, including Rb22 and p53.23 Our current results confirmed these initial observations, demonstrating loss of Rb expression in a large proportion of PLS samples. In contrast, although it has been well characterized as a tumor suppressor that inhibits progression through the cell cycle by binding to CDK4/CDK6,24, 25 we observed increased PLS p16 expression; and p16 overexpression has been demonstrated in various malignancies, including STS and specifically LPS.26 MDM2 and CDK4 are amplified in WDLPS/DDLPS as part of the 12q13-15 amplicon that has been identified in these tumors27; DDLPS samples that were included as controls on our TMA highly expressed these proteins. In contrast, only approximately 33% of PLS samples expressed CDK4, and none expressed MDM2. Clinical trials evaluating the effects of MDM2 and CDK inhibitors (eg, RO5045337 and PD0332991, respectively) on LPS currently are being initiated. Our findings do not support the inclusion of patients with PLS in the former study and call for the careful selection of patients with PLS for inclusion in the latter study. A recent study indicated that p53 was mutated more frequently in PLS compared with most other STS subtypes.16 Our data recapitulate this observation, demonstrating high rates of p53 core binding domain mutations in PLS as well as various levels of p53 protein expression. No correlation between p53 mutation status and p53 protein levels was identifiable, as demonstrated previously in other malignancies.28 Therefore, p53 immunohistochemistry cannot be used as a surrogate methodology to identify p53 mutations in PLS. Mutations of p53 contribute to chemoresistance,29 possibly explaining PLS therapeutic resistance and suggesting that reconstituting p53 function in these tumors may be fruitful.30

PPARγ is a nuclear hormone receptor that plays a critical role in adipocyte differentiation.31 Although it may seem counterintuitive given its role in differentiation, data support a PPARγ protumorigenic function.32 A recent study identified enhanced PPARγ expression in LPS subtypes, especially in MLS, DDLPS, and PLS33; our findings support this observation. It has been demonstrated that PPARγ agonists induce differentiation and growth inhibition in cancer cells that express this protein, including LPS.34-37 Initial clinical experience demonstrated significant adipocytic differentiation in 2 patients with PLS patients who were treated with the PPARγ ligand troglitazone.38 A phase 2 clinical trial in patients with LPS failed to achieve any objective clinical response, suggesting that PPARγ activation as a solitary approach is insufficient39; no patients with PLS were included in that trial. Further investigation of PPARγ as a therapeutic target for PLS appears warranted, especially in combination with the blockade of additional pathways. Molecules contributing to cancer cell survival, such as BCL2 and survivin, also have been of interest as novel therapeutic targets,40-42 and small-molecule inhibitors are being evaluated in human clinical trials. Our results demonstrate increased expression of these potential targets in PLS, especially survivin; and further preclinical investigations using human cell lines and xenograft models currently are ongoing. Similarly, we identified increased PLS expression of VEGF, the metalloproteases MMP2 and MMP9, and the tyrosine kinase receptor EGFR; and novel therapies targeting these molecules currently are available.43-45 Our study identifies several potential therapeutic targets that are overexpressed in PLS. Further preclinical investigations using relevant PLS experimental models are needed. In this study, we observed that, as expected, a single PLS tumor may exhibit multiple molecular aberrations (see Fig. 2, heat map). This reflects the molecular complexity of PLS in which a multitude of genetic and epigenetic deregulations are at play. Consequently, using novel therapeutic combinations rather than single-target therapies to block multiple pathways and processes may constitute the best anti-PLS approach.

Acknowledgements

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES

We thank Ms. Vu for aid in figure preparation and Mr. Cuevas for his assistance with article preparation and submission. We highly appreciate the philanthropic support of the Lobo, Margolis, and Jackson families.

FUNDING SOURCES

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES

This work was supported in part by the National Cancer Institute, National Institutes of Health (Grant RO1CA138345 to D.L.), by Liddy Shriver Foundation seed grants (to D.L. and D.B.), by an Amschwand Foundation seed grant (to D.L.), and by a Deutsche Forschungsgemeinschaft fellowship grant (to M.P.G.). Philanthropic support also was provided by the Lobo, Margolis, and Jackson families.

CONFLICT OF INTEREST DISCLOSURES

The authors made no disclosures.

REFERENCES

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Acknowledgements
  7. FUNDING SOURCES
  8. REFERENCES