Oncology — Canine

Boxers are predisposed to mast cell tumors, which degranulate with handling (Darier sign) and exfoliate well on FNA. Cytologic diagnosis before excision dictates surgical margins and staging. Acute collapse with hemoabdomen and a cavitated splenic mass in an older German Shepherd is most consistent with ruptured hemangiosarcoma. Hematoma is the main differential but is less likely than HSA to present with collapse in this signalment. Large and giant breeds, metaphyseal location away from the elbow and toward the knee (distal radius is classic), and an aggressive monostotic lesion respecting the joint space typify osteosarcoma. Fungal osteomyelitis is the key differential in endemic regions. Lymph node FNA is minimally invasive and usually diagnostic for multicentric lymphoma. Pre-diagnosis corticosteroids can induce partial remission, obscure diagnosis, and promote chemotherapy resistance.