CD44 has diverse functions in cell-cell and cell-matrix interactions and may be a determinant of metastatic and invasive behaviour in carcinomas. CD44 variant 6 (CD44v6) has been postulated to be involved in both carcinogenesis and tumor progression. Therefore, we have examined CD44v6 expression in tumors from 57 patients with advanced colorectal cancer who received one of two chemotherapy regimes (either irinotecan alone or irinotecan and 5-flurouracil with folinic acid). CD44v6 expression was determined immunohistochemically in 57 paraffin-embedded primary tumor sections and assessed using image analysis software. Strong expression levels of CD44v6 were seen in 24/57 (42%) of tumors, moderate levels in 17/57 (30%), weak levels in 9/57 (16%) and no expression was seen in 7/57 (12%). The pattern of staining was predominantly cytoplasmic, 7/57 tumors also exhibited membrane specific expression. A significant association was found between tumor CD44v6 expression and treatment response (Fisher's exact test p=0.01). Only 1/12 patients with no or weak tumor expression of CD44v6 showed a response to treatment whereas 20/41 (49%) patients with moderate or strong CD44v6 expression responded to treatment. Evaluation of CD44v6 expression of locally advanced and metastatic colorectal tumors may enable the clinician to identify and select patients that will show the best response to irinotecan based chemotherapy.

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