[525] Expression of P16 and MITF-1 in Acral Lentiginous/Mucosal Melanomas

EML Li-Ning-Tapia, WL Wang, JL Curry, VG Prieto, CA Torres-Cabala. UT-MD Anderson Cancer Center, Houston, TX

Background: Late research on the pathogenesis of melanoma suggests that acral lentiginous /mucosal melanomas (ALM/MuM) evolve through different mechanisms than the more frequent cutaneous melanomas. Loss of expression of p16 has been observed in melanomas occurring in intermittently sun exposed areas and may lead to cell-cycle progression. Microphthalmia transcription factor 1 (MITF-1) is a protein associated with the regulation of expression of p16. It is also considered a very sensitive marker of melanocytic differentiation. However, due in part to the scarcity of the occurrence of ALM/MuM in the United States, there is limited information on the expression of both p16 and MITF-1 in ALM/MuM.
Design: Immunohistochemistry for p16 and MITF-1 was performed on 34 sections of paraffin blocks corresponding to 22 patients with primary acral/ mucosal lentiginous melanomas showing invasive and/or in situ components, and in 9 sections of paraffin blocks corresponding to 9 patients with metastatic acral /mucosal lentiginous melanoma. Nuclear expression of p16 and MITF-1 was evaluated in the in situ and invasive components. Intensity and percentage of expression was scored.
Results: Patients with primary melanoma were 65 years old on average (35 – 87), 46.4% were male and 53.6% were female. Patients with metastatic melanoma were 66.9 years old on average (35 – 82), 55.6% were male and 44.4% were female. p16 was expressed in 91.3% (n=21) of in situ ALM/MuM, in 86.9% (n=20) of invasive ALM/MuM, and 77.8% (n=7) of metastatic ALM/MuM. MITF-1 was equally expressed in metastatic, invasive and in situ tumors.
Conclusions: There was a tendency to a loss of expression of p16 with progression of ALM/MuM. This loss of expression is similar to what has been described in the most common types of melanomas. MITF-1 was found to be a useful marker of melanocytic differentiation in ALM/MuM. In summary, in spite of the different molecular mechanisms implicated in the pathogenesis of ALM/MuM, immunohistochemical expression of p16 and MITF-1 shows similar characteristics to cutaneous melanomas of intermittently sun exposed skin.
Category: Dermatopathology

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 81, Wednesday Afternoon


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