Cytologic sampling of the ultrasonographically normal spleen and liver is not implemented routinely in the clinical staging of canine cutaneous mast cell tumors and normal ultrasound findings are often accepted as sufficient evidence for ruling out splenic or liver metastasis. Our objective was to define the specificity and sensitivity of ultrasound findings for diagnosis of mast cell infiltration when verified with cytologic evaluation, and to define the prognostic role of cytologic evaluation of liver and splenic aspirates. Dogs with a diagnosis of clinically aggressive grade II, or grade III mast cell tumor treated with a combination vinblastine/CCNU chemotherapy protocol, were selected retrospectively based on availability of cytologic evaluation of spleen plus or minus liver for staging. Out of 19 dogs, 10 dogs had a grade II tumor and nine a grade III tumor. Seven dogs had mast cell infiltration of the spleen, liver, or both. The sensitivity of ultrasound for detecting mast cell infiltration was 43% for the spleen and 0% for the liver. Dogs with positive cytologic evidence of mast cell infiltration to spleen, liver, or both had significantly shorter survival (100 vs. 291 days) than dogs without evidence of mast cell infiltration (P<0.0001). Routine splenic aspiration should be performed regardless of ultrasonographic appearance in dogs with a clinically aggressive mast cell tumor.

Conventional chemotherapeutics remain essential treatments for most cancers, but their combination with other anticancer drugs (including targeted therapeutics) is often complicated by unpredictable synergies and multiplicative toxicities. As cytotoxic anticancer chemotherapeutics generally function through induction of apoptosis, we hypothesized that a molecularly targeted small molecule capable of facilitating a central and defining step in the apoptotic cascade, the activation of procaspase-3 to caspase-3, would broadly and predictably enhance activity of cytotoxic drugs. Here we show that procaspase-activating compound 1 (PAC-1) enhances cancer cell death induced by 15 different FDA-approved chemotherapeutics, across many cancer types and chemotherapeutic targets. In particular, the promising combination of PAC-1 and doxorubicin induces a synergistic reduction in tumor burden and enhances survival in murine tumor models of osteosarcoma and lymphoma. This PAC-1/doxorubicin combination was evaluated in 10 pet dogs with naturally occurring metastatic osteosarcoma or lymphoma, eliciting a biologic response in 3 of 6 osteosarcoma patients and 4 of 4 lymphoma patients. Importantly, in both mice and dogs, coadministration of PAC-1 with doxorubicin resulted in no additional toxicity. On the basis of the mode of action of PAC-1 and the high expression of procaspase-3 in many cancers, these results suggest the combination of PAC-1 with cytotoxic anticancer drugs as a potent and general strategy to enhance therapeutic response.