Canine histiocytic sarcoma (HS) is a rare tumor originating from either interstitial myeloid dendritic antigen-presenting cells or malignant macrophages of splenic red pulp and bone marrow.1 The clinical course of HS in dogs is generally rapidly progressive with a grave prognosis for survival. Of 77 Bernese Mountain Dogs with HS, the majority of which had disseminated HS, median survival time was 30 days and <10% of dogs lived longer than 4 months.2 Even when dogs present with localized HS, the majority eventually develop disseminated disease regardless of whether or not the primary tumor is successfully removed in its entirety. Most dogs with localized HS treated with surgery alone still succumb to disease within 6 months of diagnosis.1,3 Identifying effective chemotherapeutic agents, therefore, is essential for the management of dogs with both localized and disseminated HS. When the clinical trial reported herein was initiated, publications evaluating response of HS in dogs to systemic therapies were limited. Responses to doxorubicin and liposomal doxorubicin were reported in a few cases.4 A dog with cutaneous disseminated HS temporarily responded to multiple agents, including prednisone, vincristine, cyclophosphamide, mitoxantrone, dacarbazine, and etoposide.5 Durable remissions were documented in 4 dogs with HS treated with immunotherapy consisting of a human cytotoxic T-cell line.6 A recent retrospective study evaluated CCNU [1-(2-chloroethyl)3-cyclohexyl-1-nitrosourea; lomustine] in 56 dogs with HS and reported a 46% responded for a median of 85 days. In that study, the dosage of CCNU was not uniform (dosages ranged from 60 to 90 mg/m2) and the majority of dogs received corticosteroids concurrently with CCNU.7
For inclusion into this trial, dogs were required to have nonresectable, histologically confirmed, localized, or disseminated HS. Dogs given any prior chemotherapy or glucocorticoids as therapy for HS were ineligible, as were dogs with recurrence of tumors after excision or radiotherapy. The study followed Gehan's 2-stage phase II trial design: if ≥1 antitumor response was observed among the first 9 patients in the study, then 11 additional patients would be included in the follow-up study (total of 20). If no antitumor responses were observed in the first 9 dogs treated, then there was a <10% probability of the CCNU having a true response rate of ≥25%, and case entry was stopped.8
The initial staging diagnostic evaluation included a physical examination, CBC with cytological smear evaluated by a clinical pathologist, serum biochemical profile, urinalysis, thoracic radiography, abdominal ultrasonography, and bone marrow aspiration cytology. All patients' biopsy slides were reviewed by one pathologist (coauthor, D.S.R.). Cases were confirmed as HS based on morphological features described by Affolter and Moore,1 positive immunoreactivity for CD18,a and negative immunoreactivity for lymphoid markers CD3b and PAX5.c
CCNUd was given as a single oral dosage of 90 mg/m2 body surface area every 4 weeks. CCNU is commercially available as 10, 40, and 100 mg capsules, and reformulated 5 mg capsules were prepared. Using all capsule sizes, dosage was delivered to the nearest 5 mg. After treatment with CCNU, dogs received prophylactic antibiotics (trimethoprim-sulfadiazine,e 15 mg/kg PO q12h × 14 days). A CBC was obtained 7 days after the 1st treatment. CBC and serum biochemistry were also obtained immediately before each treatment. If administration of CCNU resulted in a neutrophil count <500 cells/μL or febrile neutropenia on day 7, subsequent CCNU dosages were reduced to 70 mg/m2. Dogs underwent a complete physical examination before each treatment, and depending on the anatomical distribution of HS lesion(s), thoracic radiographs or abdominal ultrasonography were repeated before each treatment to assess response to therapy. It was planned that each dog would receive at least 1 CCNU treatment. If stable disease (SD; <50% reduction or no change in tumor volume and lack of appearance of new neoplastic lesions) was observed 2 weeks after treatment, or if there was progression of disease (PD; increase of ≥25% in tumor volume or the appearance of new neoplastic lesions or metastases) at any evaluation, clients were given the opportunity to pursue other treatment options for their dogs. Dogs that sustained a complete response (CR; resolution of all clinical signs and the disappearance of all clinical evidence of disease through at least day 28) or partial response (PR; ≥50% but <100% reduction in tumor volume through at least day 28) were scheduled to receive CCNU every 4 weeks for a total of 6 months (7 total treatments).
All dogs that began treatment with CCNU were considered for use in estimating response to therapy. Dogs that received treatment and died (regardless of cause) or were lost to follow-up before 28 days were considered treatment failures. Response duration was calculated by the Kaplan-Meier method and was defined as the number of days from the date a response was observed until relapse (for dogs that achieved CR) or PD (for dogs that achieved PR). Dogs still in remission, dogs lost to follow-up, and dogs that died of some intercurrent disease were included in response analyses until the last day follow-up information was collected and then were censored.
After documentation of 2 responses in the 1st stage of accrual, the study went to completion of the 2nd stage. Twenty-one dogs with HS were treated with CCNU between March 1999 and October 2008. Ten dogs were male and 11 were female. There were 6 Golden Retrievers, 5 Bernese Mountain Dogs, 3 Rottweilers, 3 Labrador Retrievers, 2 Flat-Coated Retrievers, and 2 other purebred dogs. The median body weight was 36 kg (range, 19–50 kg) and the median age was 8 years (range, 3–11 years).
Common clinical signs before CCNU treatment included lethargy (n = 9), inappetance (8), dyspnea (5), lameness (4), vomiting (3), and fever (1). Dogs frequently had >1 clinical sign. Nine dogs presented only for evaluation of 1 or more subcutaneous (SC) masses. Common abnormal results of clinicopathologic testing included anemia (median PCV, 42%; PCV<42% in 10 dogs), thrombocytopenia (median count, 309,000 platelets/μL; <179,000 platelets/μL in 16 dogs), hypoalbuminemia (median, 3.2 g/dL; albumin <3.1 g/dL in 8 dogs), and hypercalcemia (calcium >11.6 mg/dL in 4 dogs). Fourteen dogs had disseminated HS and 7 dogs had localized HS (Table 1).
|Classification||Sites Affected||No. of Dogs|
|Spleen, regional LN||1|
|Disseminated||Spleen, liver, abdominal LNs||3c,d|
|Spleen, abdominal LNs||2g,h|
|Lung, thoracic LNs, adrenal gland||1|
|Lung, liver, kidney, bicavitary neoplastic effusion||1|
All 21 dogs in the study received a median of 1 CCNU treatment (range, 1–5). Fourteen dogs received 1 treatment, 1 dog received 2 treatments, 2 dogs received 3 treatments, 3 dogs received 4 treatments, and 1 dog received 5 treatments. Because of rounding of reformulated CCNU capsules, the actual starting 90 mg/m2 dosage ranged from 83 to 90 mg/m2 (median, 85 mg/m2). After the 1st dose of CCNU, CBCs were evaluated on day 7 in 20 dogs. The median neutrophil count on day 7 after CCNU was 786 cells/μL (range, 0–8,360 cells/μL); neutrophil counts were < 500 cells/μL in 6 dogs. Two dogs, each with 0 neutrophils/μL, developed fever 7 days after treatment with CCNU. Both dogs recovered in ≤3 days with supportive treatment consisting of IV fluid administration and antibiotics. Increase in serum alanine transaminase, suggestive of hepatotoxicity, occurred in 2 dogs after the 1st CCNU dose (599 and 691 U/L, respectively; reference range, 25–106 U/L). Of these 2 dogs, 1 had disseminated HS and experienced PD after treatment so additional doses were not given. The other had a localized HS with regional lymph node metastases and achieved a CR; CCNU was discontinued and duration of CR (with no other therapies) was 269 days.
Six of the 21 (29%; 95% confidence interval [CI], 14–50%) dogs had a CR or PR after treatment with CCNU; the remaining dogs had PD (n = 10) or SD (n = 5). Median duration of the response was 96 days (range, 54–269 days; 95% CI, 55–137 days). All responders relapsed during the follow-up period. Three dogs had a CR. One of these dogs had disseminated HS and duration of CR was 54 days. One dog had a localized SC HS and duration of CR was 153 days. The final dog had a localized SC HS with lymph node metastasis. Duration of CR in this dog was 269 days. Three dogs had a PR for 78–112 days. Two of these dogs had disseminated HS and 1 had localized SC HS with lymph node metastasis (Fig 1).
Survival time was not a major endpoint of this study but median Kaplan-Meier survival time (from initiation of CCNU until death) was 124 days (range, 7–482 days; 95% CI, 40–208 days). Nineteen dogs died or were euthanized because of tumor-associated reasons and 2 were lost to follow-up 37 and 39 days, respectively, after beginning treatment. Five dogs did not receive any additional treatments after failing treatment with CCNU. Three dogs received prednisonef and failed to respond. The remaining 13 dogs were treated with a sequential protocol of prednisone, vincristine,g doxorubicin,hl-asparaginase,i and cyclophosphamide.j Three of these dogs (including 1 dog that had an initial PR to CCNU) achieved a PR for 28, 42, and 84 days, respectively. The remaining 10 dogs had PD (including the 5 dogs that had SD after CCNU).
Results of the present study suggest CCNU has antitumor activity in dogs with HS when administered as a single agent at 90 mg/m2 and support the use of CCNU when disseminated disease is present and local treatment is not possible. The response rate (29%; 95% CI, 14–50%) and response duration (median, 96 days; 95% CI, 55–137 days) is not importantly different from that reported in a recent study. A retrospective evaluation of CCNU in 56 dogs with HS showed a 46% response rate for a median of 85 days; dogs that had splenic involvement, were anemic (PCV<30%), or were thrombocytopenic (platelets <100,000/μL) were less likely to respond.7 In that study, however, the majority received corticosteroids concurrently with CCNU, making a direct comparison with results reported here problematic. Also, the dosage of CCNU in that study was not uniform and ranged from 60 to 90 mg/m2; whether or not a dose-response relationship existed could not be determined from the results.7 The present study was not designed or powered to analyze the impact of individual variables on response rate (or duration). Interestingly, however, only 1 dog in the current study had PCV<30% and no dogs had severe thrombocytopenia.
The study was designed to give dogs at least 1 dose of CCNU; if only SD was observed within 4 weeks, dogs could be removed from the study and be given alternative therapies. This was done because at the time of initiating the trial, the clinical presentation of HS was known to mimic a common hematopoietic malignancy, multicentric high-grade lymphoma, so it was assumed its responsiveness to chemotherapy would be analogous (ie, rapid). However, it is possible that the pattern of chemo-responsiveness of HS might be more similar to solid, nonhematopoietic tumors. The log-cell kill hypothesis suggests that for some chemotherapy drugs, the relationship between cell survival and dose is close to exponential, so that a constant fraction of the cancer cells is killed by a single dose of a drug. Sequential treatments would be needed to successfully reduce tumor populations and achieve clinical remission. Based on this theory, for the 5 dogs with SD that were removed from the study, additional CCNU treatments might have led to a remission. However, given the rapid clinical course and overall guarded prognosis associated with HS, the study was designed to allow patients to exit the study while they were hopefully still good candidates for other potential therapies, even if this meant underestimating the true efficacy of CCNU.
Clinical impact of adjuvant CCNU in the management of dogs with localized HS has not been clearly defined. Sixteen dogs with HS treated with aggressive local therapy and adjuvant CCNU were retrospectively evaluated and their median disease-free interval was 243 days. Despite the occurrence of local relapse in 2 of the dogs and metastasis in 8, the overall median survival was 568 days.9 The benefit of multimodality therapy (surgery, radiotherapy, and chemotherapy with CCNU) for dogs with metastatic HS or disseminated HS has only recently been suggested. Median survival time of 8 dogs treated with radiotherapy and CCNU was 208 days compared with 68 days for 23 dogs treated with surgery only, radiotherapy only, or a combination of radiotherapy and chemotherapy protocols that did not include CCNU.10 However, multiple sarcomas in that study were interpreted to be of histiocytic origin based only on cytopathological morphology and were not confirmed with immunohistochemical staining.10 Additional controlled studies should be conducted to evaluate the effectiveness of CCNU for dogs with HS treated in adjuvant and multimodality settings.