Primary pulmonary histiocytic sarcoma in dogs: A retrospective analysis of 37 cases (2000-2015).

Primary pulmonary histiocytic sarcoma (PHS) has been reported, but is not well characterized. The aim of this retrospective study was to describe clinical characteristics, characterize prognostic factors and report the outcome of a larger group of dogs with primary PHS. Medical records of dogs diagnosed with primary PHS at 11 institutions were retrospectively reviewed. Thirty-seven dogs were included; 13 received CCNU-based chemotherapy alone, 18 received surgery and adjuvant CCNU-based chemotherapy, 3 received medical management alone and 3 dogs received surgery alone. The overall median progression free survival (PFS) and the median survival (overall survival [OS]) were 197 and 237 days, respectively. Measurable responses were noted in dogs receiving only chemotherapy; however, responses were not durable with PFS (91 days) and OS times (131 days) shorter than overall medians. Dogs that received surgery and chemotherapy had significantly prolonged PFS (276 days, P = 0.001) and OS (374 days, P = 0.001), compared with dogs not receiving surgery. As only three dogs undergoing surgery did not receive chemotherapy, it is not possible to determine the contribution of chemotherapy as an adjuvant to surgery. Dogs without evidence of intra-thoracic metastatic disease were much more likely to undergo surgery (odds ratio = 7.04; P = 0.018). While the presence of metastasis or clinical signs at diagnosis negatively impacted PFS, only the former negatively impacted OS. These data imply that dogs presenting with PHS amenable to surgery (ie, no clinical evidence of metastasis) benefit from surgical intervention; however, the lack of a comparable surgery alone group precludes assessment of the efficacy of post-surgical adjuvant chemotherapy.