c-kit expression in dedifferentiated and well-differentiated liposarcomas; immunohistochemistry and genetic analysis

Background: c-kit expression by immunohistochemistry has been utilized to identify cancer patients who can be treated with imatinib-mesylate. In gastrointestinal stromal tumors (GISTs), an activating mutation in c-kit predicts treatment response; its presence in other soft tissue tumors is unexplored. Materials and Methods: We evaluated seven cases of dedifferentiated liposarcomas (DDLS) and compared those with seven well-differentiated liposarcomas (WDLS). Immunohistochemical staining for c-kit was performed using a polyclonal antibody. Using PCR, exons 9, 10-11, 12-13 and 17 of c-kit were amplified and direct DNA sequencing performed. Results: Two out of 7 (30%) DDLS showed focal weak immunoreactivity with c-kit; no (0%) WDLS stained with c-kit. Seven out of 7 (100%) DDLS showed an allelic variation in exon 10, with a single base pair substitution (A>C) at codon 541; 3/7 (43%) WDLS showed the same change. Conclusion: c-kit immunoreactivity did not correlate with the change in DNA sequence; DDLS showed a consistent allelic variation in c-kit that may have significant prognostic, diagnostic and therapeutic implications.