Immunohistochemical Differentiation and Clinicopathological Features of Canine Gastrointestinal Stromal Tumors and Leiomyosarcomas

Introduction:  Gastrointestinal stromal tumors (GIST) and leiomyosarcomas (LMS) have recently been differentiated by immunohistochemical staining techniques and have been shown to have different biological behaviors in humans. Expression of the c‐kit protein, a transmembrane tyrosine kinase receptor, occurs in nearly all GISTs. The aim of this study was to differentiate canine GIST from LMS, and to compare their clinicopathological features.
Methods:  Archived blocks of previously diagnosed LMS were analyzed. Immunohistochemical staining using antibodies against c‐kit, smooth muscle actin (SMA), desmin, vimentin and S100 was performed. GISTs were diagnosed based on positive c‐kit staining. LMS were diagnosed based on absence of c‐kit staining and positive SMA staining. Follow‐up information was obtained from medical records and telephone interviews with owners.
Results:  Forty‐two dogs were included in the study. Mean age was 10.9 yrs (range 5–15 yrs). There were 18 females and 24 males. Twenty‐eight tumors were GISTs, 10 were LMS and 4 stained negatively for c‐kit, SMA and S100 (sarcomas). GISTs were more likely to occur in the large intestine and LMS were more common in the small intestine (p = 0.01). All were surgically excised and only two were treated with adjunctive chemotherapy. Only two GISTs and one sarcoma had metastasized at the time of surgery. Survival time in dogs discharged after surgery for GIST, LMS and sarcomas was 1123, 233 and 88 days respectively (p = 0.08).
Conclusions:  Many previously diagnosed LMS should be reclassified as GIST based on the results of immunohistochemical staining. The biological behavior of these tumors appears to be different.