Abstract
Leiomyosarcoma (LMS) of the colo-rectum is a rare malignant entity with unfavourable prognosis, and responds poorly to conventional chemo-radiation therapy. Only a few cases of the LMS of colorectum have so far been reported earlier. Here we report two such cases of primary leiomyosarcoma of sigmoid colon and rectum. Due to histological similarity with gastrointestinal stromal tumour (GIST), the LMS cases were misdiagnosed as GIST. This is essentially a pathological diagnosis having a similar histomorphological appearance that of GIST, but a different Immunohistochemistry profile, in contrast to GIST. Immunohistocytochemically LMS are negative for CD34, CD117 and DOG1 and positive for desmin as detected in this report. GIST is curable with surgery followed by imatinib (in intermediate /high-risk patients) while LMS behaves aggressively requiring radical excision of the tumour followed by intensive cytotoxic chemotherapy regimens. Thus it is important to diagnose LMS definitively by immunohistochemical profiling as the prognosis and treatment of these tumours vary from others as mentioned.

Key words: Leiomyosarcoma, colon, rectum, Immunohistochemistry, Rare case