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Keywords:

  • lung carcinoma;
  • hypercalcemia;
  • bone metastases;
  • prognosis;
  • parathyroid hormone-related protein (PTH-rP);
  • interleukin-6 (IL-6)

Abstract

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

BACKGROUND

Parathyroid hormone-related protein (PTH-rP) is a major cause of tumor-induced hypercalcemia (TIH) and frequently is found to be elevated in serum of patients with TIH. In the current study, the authors examined the usefulness of PTH-rP measurement at the time of first presentation in the follow-up of lung carcinoma patients with TIH.

METHODS

The authors retrospectively studied 23 of 1149 lung carcinoma patients who were found to have TIH at the time of first presentation for the correlation between serum PTH-rP and the development of bone metastases and survival compared with lung carcinoma patients without TIH who were matched by gender, age, Eastern Cooperative Oncology Group performance status, histological type of tumor, and stage of the disease.

RESULTS

Twenty-three lung carcinoma patients with TIH demonstrated significantly increased serum levels of PTH-rP (mean ± standard error [SE], 84.1 ± 16.5 pmol/L) compared with control patients without TIH (mean ± SE, 36.2 ± 2.0 pmol/L) at the time of first presentation, (P < 0.001). In these hypercalcemic patients, patients whose serum PTH-rP was > 150 pmol/L (n = 16) were found to have a significantly increased rate of bone metastases (71.4% vs. 12.5%; P = 0.01) and decreased survival (median survival of 1.4 months vs. 5.4 months; P < 0.015) compared with patients whose serum PTH-rP was < 150 pmol/L (n = 7).

CONCULUSIONS

The data from the current study suggest that serum PTH-rP as determined at the time of first presentation is a useful indicator of not only hypercalcemia but also bone metastasis and eventual survival in patients with lung carcinoma. Cancer 2002;95:1706–13. © 2002 American Cancer Society.

DOI 10.1002/cncr.10828

The treatment course of patients with cancer frequently is complicated with ectopic hormonal syndromes or paraneoplastic syndromes such as hypercalcemia, leukocytosis, and hyponatremia as well as Cushing syndrome.1, 2 Among these, tumor-induced hypercalcemia (TIH) is one of the most common paraneoplastic syndromes and usually occurs at the advanced and/or terminal stage of the illness.3 TIH progressively causes diverse clinical symptoms, such as nausea, unconsciousness, and coma, that profoundly affect the morbidity and eventual mortality of patients with cancer.3, 4 To treat and manage TIH in a timely and appropriate manner, the development of a serum marker that reliably reflects the state of TIH is very useful. It generally has been recognized that increased bone resorption is the primary cause of TIH.5 Evidence has accumulated that parathyroid hormone-related protein (PTH-rP), which is a potent stimulator of bone resorption, is responsible for inducing TIH.5 Clinical studies have reported that approximately 80% of hypercalcemic patients with solid tumors exhibit increased blood levels of PTH-rP.6 Consistent with these clinical studies, it was demonstrated that several human tumors that produce substantial amounts of PTH-rP caused hypercalcemia when implanted into nude mice and that the neutralizing antibodies to PTH-rP reversed the TIH in these tumor-bearing animals.7, 8 Accordingly, PTH-rP has been recognized as one serum marker with which to monitor the state of TIH and evaluate the effectiveness of treatment in cancer patients.6 Because PTH-rP was measured during the clinical course in these studies, it remains unknown whether these patients initially manifest elevated levels of blood PTH-rP and, if so, whether the PTH-rP serum level determined at the time of first presentation is correlated with the subsequent clinical course of these cancer patients with TIH.

In the current study, we examined 23 of 1149 patients with lung carcinoma who manifested TIH at time of first presentation, a tumor known to be associated most frequently with TIH4, 9 in a retrospective manner and examined whether serum PTH-rP determined at the time of first presentation could serve as an indicator for bone metastasis and survival. We specifically examined the relation between serum levels of PTH-rP and bone metastases because lung carcinoma has a strong predilection for spreading to bone10 and PTH-rP is implicated in bone metastases in malignancies such as breast carcinoma.5 Our data confirm that PTH-rP is elevated in lung carcinoma patients with TIH. Moreover, the results of the current study also demonstrate a significant correlation between elevated serum levels of PTH-rP and increased bone metastasis and shorter survival in lung carcinoma patients with TIH.

MATERIALS AND METHODS

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

Patients

This retrospective study included 1149 inpatients with lung carcinoma who were treated at the Okayama University Hospital and National Shikoku Cancer Center between 1986 and 1996. The clinical features of these patients are summarized in Table 1. There were 871 men and 278 women, with a median age of 66 years (range, 20–92 years).

Table 1. Patient Characteristics
 TotalSerum calcium level
≥ 10.2 (%)< 10.2
  1. ECOG: Eastern Cooperative Oncology Group; PS: performance status; NSCLC: nonsmall cell lung carcinoma; SCLC: Small cell lung carcinoma.

No. evaluated1149651084
Median age (yrs)666766
 (range)20–9245–9220–92
Gender:   
 Male87159812
 Female2786272
ECOG PS:   
 03324328
 156123538
 212212110
 3881771
 446937
Histlogy:   
NSCLC83554781
 Adenocarcinoma44214428
 Squamous cell carcinoma32433291
 Large cell carcinoma55550
 Adenosquamous cell carcinoma14212
SCLC29410284
Others20119
Clinical stage   
 I1514147
 II77473
 IIIA1788170
 IIIB26622244
 IV47727450

The histologic type of lung tumors studied was classified into adenocarcinoma (442 cases), squamous cell carcinoma (324 cases), large cell carcinoma (55 cases), and small cell carcinoma (294 cases) according to the World Health Organization (WHO) classification.11

Collection of Sera

Blood samples for cytokine determination were collected at the time of the first visit of these patients, before they received any treatments. Serum was separated immediately and stored until assays were performed.

Diagnosis of Hypercalcemia

Hypercalcemia was defined as a serum calcium (Ca) concentration > 10.2 mg/dL after adjustment for the serum albumin concentration. When the serum albumin concentration was < 4.0 g/dL, the Ca value was adjusted as: adjusted Ca concentration (g/dL) = measured Ca concentration + 4.0 − albumin concentration.

Evaluation of Bone Metastases

All patients with lung carcinoma were examined for bone metastases at the time of their first visit using 99mTc-MDP. When the presence of bone metastases was suspected, further examination by X-ray, computed tomography (CT), and magnetic resonance imaging (MRI) was conducted to verify bone metastases.

Determination of Serum Concentrations of C-PTH-rP, Immunoreactive-PTH, Interleukin-1β, Interleukin-6, and Tumor Necrosis Factor-β

C-PTH-rP (109 to 141 from N-terminus) was measured with C-terminal region specific radioimmunoassay using commercially available kits (Daiichi RI Laboratory, Tokyo, Japan). Serum concentrations of C-PTH-rP in healthy subjects ranged from 13.8–55.8 pmol/L using this kit. Immunoreactive parathyroid hormone (I-PTH) was measured with a two-site immunoradiometric assay (IRMA) using commercially available kits (detection limit: 3 pmol/L; Nippon Mejifix, Tokyo, Japan). Interleukin-1β (IL-1β) was measured with an IRMA using commercially available kits (Medgenix, Fleurus, Belgium). Interleukin-6 (IL-6) and tumor necrosis factor-β (TNF-β) were measured using commercially available enzyme-linked immunoadsorbent assay kits (Otsuka, Tokyo, Japan).

Statistical Analysis

The chi-square test or trend test was used to analyze the correlation between the serum Ca concentration and several categoric variables. Probabilities of survival were estimated using the Kaplan–Meier method and differences between patient groups were determined by the log-rank test. All reported P values are two-sided. Prognostic factors were analyzed using the Cox proportional hazards model. A P level of < 0.05 was considered to be statistically significant.

RESULTS

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

TIH in Lung Carcinoma Patients

The current retrospective study of the clinical records revealed that 65 of 1149 patients with lung carcinoma (5.7%) manifested TIH at the time of their first presentation to the study clinics. Of these 65 patients, 57 already had advanced stage disease (Stage III and IV) at the time of their first visit.

Although the frequency of TIH in our clinics is lower than what has been reported previously for lung carcinoma patients (range, 12.5–35%),4, 9 it should be noted that the current study data represent the frequency of TIH in lung carcinoma patients at the time of their first presentation.

The relation between TIH and clinicopathologic factors is shown in Table 2. There was a significant correlation between TIH and gender (P < 0.01), ECOG PS (P < 0.001), leukocyte count (LC) (P < 0.001), and serum creatinine concentration (P < 0.001). Male patients were found to have TIH more frequently than female patients. The frequency of TIH also was found to be increased in patients with a worse ECOG PS, an increased LC, or increased serum levels of creatinine. Histologic examination showed that TIH occurred in all types of lung carcinoma. However, squamous cell carcinoma was associated most frequently with TIH (10.2%).

Table 2. Relation between Serum Calcium Level and Clinicopathologic Factors
FactorSerum calcium levelP value
≥ 10.2< 10.2
  1. ECOG: Eastern Cooperative Oncology Group; PS: performance status; NSCLC: non small cell lung carcinoma; SCLC: small cell lung carcinoma; NS: not Significant; LC: leukocyte count.

Gender:   
 Male59812 
 Female6272< 0.01
ECOG PS:   
 0–127866 
 2–438218< 0.001
NSCLC + SCLC   
 Squamous cell carcinoma33291 
 Non-squamous cell carcinoma32793< 0.001
NSCLC   
 Squamous cell carcinoma33291 
 Non-squamous cell carcinoma22490< 0.001
Clinical stage   
 I–II8220 
 III–IV57864NS
Bone metastasis   
 Present20215 
 Absent45869< 0.05
LC   
 ≥ 12,000/mm31766 
 < 12,000/mm3481018< 0.001
Creatinine   
 ≥ 1.25 mg/dL1381 
 < 1.25 mg/dL521003< 0.001

All 1149 lung carcinoma patients were monitored routinely each month by chest X-ray and blood examination. Figure 1 clearly demonstrates that survival was significantly shorter in patients with TIH (median survival time [MST] of 3.5 months; n = 65) compared with patients without TIH (MST of 9.5 months; n = 1084) (P < 0.001).

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Figure 1. Relation between serum levels of serum calcium (Ca) and overall survival in lung carcinoma patients (Kaplan–Meier analysis). Serum Ca was measured at the first visit of all patients (1149 cases). Patients whose serum Ca levels were > 10.2 mg/dL after adjustment for serum albumin concentrations were diagnosed as having tumor-induced hypercalcemia (TIH). Survival was found to be significantly shorter in patients with TIH (dotted line; median survival time of 3.5 months, [n = 65]) compared with patients without TIH (solid line; median survival time of 9.5 months [n = 1084]) (P < 0.001).

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Multivariate analysis of prognostic factors using the Cox proportional hazards model revealed that ECOG PS (P = 0.0001), clinical stage (P = 0.0001), gender (P = 0.0001), serum Ca concentration (P = 0.0001), serum albumin concentration (P = 0.0001), serum lactate dehydrogenase concentration (P = 0.0021), and LC (P = 0.0087) appeared to have independent prognostic significance. Serum concentration of creatinine (P = 0.9483), histologic type of tumor (P = 0.3095), and patient age (P = 0.6900) did not appear to have any significant effect on survival (Table 3).

Table 3. Multivariate Analysis of Prognostic Factors
 VariablesHR95% CIP value
  1. HR: hazards ratio; 95% CI: 95% confidence interval; ECOG: Eastern Cooperative Oncology Group; PS: performance status; LDH: lactate dehydrogenase; LC: leukocyte count; SCLC: small cell lung carcinoma; NSCLC: nonsmall cell lung carcinoma.

ECOG PS0–2vs. 3–4(1015 vs. 134)2.001.69–2.360.0001
StageI–IIvs. III–IV(228 vs. 921)1.851.57–2.100.0001
GenderMalevs. female(871 vs. 278)1.491.25–1.770.0001
Calcium≥10.2 mg/dLvs. < 10.2 mg/dL(65 vs. 1084)1.771.34–2.350.0001
Albumin≥ 4.0 g/dLvs. < 4.0 g/dL(462 vs. 687)1.351.17–1.570.0001
LDH≥ 450 IU/Lvs. < 450 IU/L(283 vs. 866)1.281.09–1.500.0021
LC≥ 7000/mm3vs. < 7000/mm3(533 vs. 616)1.211.04–1.390.0087
Creatinine≥ 1.04 mg/dLvs. <1.04 mg/dL(275 vs. 874)1.010.86–1.180.9483
HistologySCLCvs. NSCLC(294 vs. 855)1.080.93–1.260.3095
Age (yrs)≥ 70vs. < 70(394 vs. 755)1.030.89–1.190.6900

Correlation between Serum Levels of C-PTH-rP, I-PTH, IL-1β, IL-6, or TNF-β and Occurrence of TIH

We studied 23 patients with TIH who had complete laboratory data with regard to C-PTH-rP, I-PTH, IL-1β, IL-6, and TNF-β of 65 patients who were found to have TIH at the time of first presentation and compared them with 23 patients without TIH who were matched by gender, age, ECOG PS, histologic type of tumor, and stage of the disease.

Serum concentrations of C-PTH-rP as determined at the time of first presentation were found to be elevated significantly in patients with TIH compared with patients who did not manifest TIH (84.1 ± 16.5 pmol/L vs. 36.2 ± 2.0 pmol/L [mean ± Standard error (SE)]; P < 0.001) (Fig. 2A).

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Figure 2. Serum concentrations of (A) parathyroid hormone-related protein (PTH-rP) and (B) interleukin-6 (IL-6) determined at the first visit of lung carcinoma patients with (n = 23) or without (n = 23) having tumor-induced hypercalcemia (TIH). They were matched by gender, age performance status, histologic type of lung tumor, and stage of the disease. In Panel A, serum levels of C PTH-rP were elevated significantly in patients with TIH compared with patients without TIH (84.1 ± 16.5 pmol/L vs. 36.2 ± 2.0 pmol/L mean ± Standard error [SE]; P < 0.001). The highest serum PTH-rP value noted in a hypercalcemic In Panel B, serum levels of IL-6 also were significantly higher in patients with hypercalcemia compared with patients without hypercalcemia (35.5 ± 7.2 pg/mL vs. 2.8 ± 0.7 pg/mL [mean ± SE]; P < 0.001). The highest serum IL-6 value noted in a hypercalcemic lung carcinoma patient was 166 pg/mL. The bar in the graph represents the mean value.

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In addition to PTH-rP, we also measured serum levels of other bone-resorbing cytokines including PTH, TNF-β,12, 13 IL-1β14 and IL-615 in the sera collected at the time of the first presentation of these patients. These cytokines also are implicated in the pathogenesis of TIH. Furthermore, IL-1β16, 17 and IL-618 have been shown to enhance PTH-rP-induced bone resorption and hypercalcemia. Of note, these hypercalcemic patients also exhibited higher serum levels of IL-6 compared with nonhypercalcemic patients (35.5 ± 7.2 pg/mL vs. 2.8 ± 0.7 pg/mL [mean ± SE]; P < 0.001) (Fig. 2B). Serum levels of IL-1β were not found to be increased in patients with TIH compared with patients without TIH (data not shown).

Serum levels of I-PTH and TNF-β were reported to be within the normal range or below the detection limit (< 156 pg/mL), respectively, in all the patients studied herein (data not shown).

Correlation between Serum Levels of PTH-rP and Frequency of Bone Metastasis

Because lung carcinoma patients most frequently develop bone metastases and PTH-rP is implicated in the pathogenesis of bone metastasis,5 we examined the relation between serum PTH-rP and the occurrence of bone metastases in the 23 hypercalcemic lung carcinoma patients in the current study. The data showed that bone metastases were increased significantly in hypercalcemic lung carcinoma patients whose serum levels of PTH-rP were > 150 pmol/L (71.4%) compared with hypercalcemic lung carcinoma patients whose serum PTH-rP levels were < 150 pmol/L (12.5%) (P = 0.01) (Fig. 3). When we analyzed the relation between bone metastasis and a serum PTH-rP level < 150 pmol/L, we were unable to find a correlation. The relation between PTH-rP and the frequency of bone metastasis in lung carcinoma patients without TIH is unknown, because serum PTH-rP was not measured routinely in nonhypercalcemic lung carcinoma patients at the time of the first visit. There was no apparent correlation between serum levels of IL-6 and the frequency of bone metastases (data not shown).

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Figure 3. Relation between serum levels of parathyroid hormone-related protein (PTH-rP) determined at the time of first presentation and overall survival in lung carcinoma patients with tumor-induced hypercalcemia (TIH) (Kaplan–Meier analysis). Patients with TIH who had serum levels of PTH-rP > 150 pmol/L (dotted line) exhibited significantly shorter overall survival than those whose serum PTH-rP levels were < 150 pmol/L (solid line) (P < 0.015). The numbers in parentheses indicate the number of patients studied.

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Correlation between Serum Levels of C-PTH-rP and Survival in Patients with TIH

We next examined the relation between serum levels of PTH-rP and survival in the 23 patients with TIH. As shown in Figure 4, survival in hypercalcemic lung carcinoma patients with serum PTH-rP levels > 150 pmol/L was significantly decreased compared with that in patients with a serum PTH-rP level < 150 pmol/L (MST of 1.4 months vs. 5.4 months; P < 0.015). There was no apparent correlation between serum levels of IL-6 and survival in these patients (data not shown).

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Figure 4. Relation between serum levels of parathyroid hormone-related protein (PTH-rP) and frequency of bone metastasis in lung carcinoma patients with tumor-induced hypercalcemia. Serum levels of PTH-rP were determined at the time of first presentation in these patients. Bone metastases were detected as described in the text. The numbers in parentheses indicate the percentage of total patients. Hypercalcemic patients with serum PTH-rP levels > 150 pmol/L demonstrated a significantly increased frequency of bone metastases (71.4%) compared with those whose serum PTH-rP levels were < 150 pmol/L (12.5%) (P = 0.01).

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DISCUSSION

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

It is well established that PTH-rP is a major bone-resorbing factor that is responsible for TIH in patients with a variety of malignancies including carcinomas of the lung, breast, and head and neck.5, 19–21 In the current study, we found that profoundly elevated serum levels of PTH-rP (> 150 pmol/L) measured at the time of the first visit were correlated with an increased frequency of bone metastases and shorter survival in lung carcinoma patients with TIH. These results suggest that PTH-rP measured at the time of first presentation is an indicator not only of TIH but also bone metastasis and eventual survival in patients with lung carcinoma. The results of the current study also suggest that serum PTH-rP as determined at the first visit provides useful information for predicting the subsequent clinical course of lung carcinoma patients with TIH.

Lung carcinoma has been known to have a predilection for spreading to bone.10 Recent studies suggest that PTH-rP plays a critical role in tumor invasion and distant metastasis22, 23 and facilitates dissemination of breast and prostate carcinoma to bone.6, 24–26 These previous observations led us to determine the relation between serum levels of PTH-rP and the development of bone metastases in lung carcinoma patients with TIH. Data from the current study demonstrate that bone metastases are increased in lung carcinoma patients with TIH who have serum levels of PTH-rP > 150 pmol/L at the time of first presentation (normal range of PTH-rP in our institutions was 13.8–55.8 pmol/L). Although only a small number of lung carcinoma patients with TIH was studied herein, the results suggest that PTH-rP could be a serum marker of bone metastases as well as hypercalcemia in lung carcinoma patients.

To our knowledge, the reason that hypercalcemic lung carcinoma patients with serum levels of PTH-rP < 150 pmol/L exhibit shorter survival is unknown. Increased bone metastases are a potential cause of a short lifespan. Decrease in food intake due to TIH4 could be another reason. In addition, PTH-rP has been shown to play a role in causing cachexia in tumor-bearing mice.5 Alternatively, several previous studies have demonstrated that PTH-rP is an autocrine growth factor for tumors such as rat Walker 256 carcinoma27 and BEN human lung carcinoma,28 both of which are associated with hypercalcemia. More recently, it has been reported that PTH-rP promotes the progression and metastases of rat malignant pituitary tumor23 and human prostate carcinoma.26 It is conceivable that the growth and distant metastases of lung tumors are promoted by the direct effects of PTH-rP, which in turn leads to decreased survival in lung carcinoma patients with TIH.

It would be very useful if the existence of bone metastases could be diagnosed and survival predicted by the determination of serum markers in cancer patients. The results of the current study demonstrating that PTH-rP > 150 pmol/L is correlated significantly with the presence of bone metastasis and shorter survival suggest that PTH-rP measured at the time of first presentation could be such a marker and that 150 pmol/L might be a critical value with which to make diagnosis of bone metastasis and predict survival. We established the value of 150 pmol/L by serially conducting statistical analyses of the correlation of various serum levels of PTH-rP with bone metastases and survival. Further extensive studies including greater numbers of patients are needed to verify whether this is truly the case in lung carcinoma patients with TIH.

It is interesting to note that the current study data also demonstrate that lung carcinoma patients with TIH exhibit increased serum levels of IL-6 compared with those without TIH. Increased blood levels of IL-6 occasionally are detected in patients with hematologic malignancies such as myeloma.29, 30 However, to our knowledge only a limited number of cases of solid tumors have been reported to be associated with elevated serum levels of IL-6.15 The current study data suggest that IL-6 as well as PTH-rP play a role in TIH in lung carcinoma. We assume that increased serum levels of IL-6 are the result of overproduction of IL-6 by lung tumors as reported previously in squamous carcinoma cases.15 Although it has been reported that IL-6 production is stimulated by PTH-rP,31 we believe that the production of IL-6 in lung carcinoma is independent of PTH-rP, because IL-6 has no correlation with bone metastasis such as PTH-rP does. Thus, it is suggested that IL-6 independently causes TIH and additively or synergistically enhances it in cooperation with PTH-rP. Consistent with this notion, de la Mata et al. have demonstrated that IL-6 enhances PTH-rP-induced hypercalcemia in human lung carcinoma.16 However, regardless of the role IL-6 plays in TIH, the results of the current study suggest that serum IL-6 is an additional indicator for TIH in patients with lung carcinoma.

The results of the current study demonstrate that elevated serum levels of PTH-rP are correlated with an increased likelihood of bone metastases and shorter survival in lung carcinoma patients with TIH and suggest that the determination of serum PTH-rP at the time of first presentation also is informative for the follow-up of lung carcinoma patients with TIH as has been reported previously in hypercalcemic patients with other malignancies.

Acknowledgements

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

The authors thank Dr. Gregory R. Mundy, Division of Endocrinology and Metabolism, Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas for his careful reading of this article.

REFERENCES

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