[427] KBA.62 and KIT Expression Patterns in Fine-Needle Aspirates of Malignant Melanoma Metastatic to the Liver.

Sinchita Roy Chowdhuri, Patricia Fetsch, Marybeth S Hughes, Armando C Filie. National Cancer Institute, Bethesda, MD

Background: KBA.62 has been described as a useful marker for diagnosing primary and metastatic malignant melanomas (MMM) in tissue. We stained fine-needle aspirates (FNA) of MMM to the liver for KBA.62 and compared it to standard melanoma markers, Mart-1 and HMB-45. Recent studies have shown that correlation between percentage of KIT-positive cells by IHC and KIT mutation status in MMM may be an important predictor of response to imatinib mesylate therapy. Since a large number of these metastatic tumors have been reported to express KIT, we also examined the liver FNAs for KIT expression.
Design: 22 cases of FNAs of MMM to the liver were retrieved from our files. Morphological examination of direct smears by Diff-Quik and Papanicolaou stains, as well as hematoxylin-eosin stained cell blocks was performed. Immunohistochemical (IHC) stains were evaluated using standard melanoma markers, Mart-1 and HMB-45, along with stains for KBA.62 and KIT. KIT expressing tumors were also evaluated for percentage of positive tumor cells. For cases negative for Mart-1 and HMB-45, additional IHC stains for S-100 and cytokeratin were performed.
Results: From the 22 cases reviewed, 21 (95.5%) stained positive for Mart-1 and 18 (81.8%) stained positive for HMB-45. 16 tumors (72.7%) stained positive for KBA.62 (strong membranous pattern), and 9 tumors (40.9%) stained positive for KIT (mostly showing cytoplasmic staining with membranous accentuation). 2 out of 9 cases showed KIT expression in >75% of tumor cells while 5 out of 9 cases had KIT expression in <25% of tumor cells. 4 cases that were negative for one or both melanoma markers (Mart-1 and HMB-45) were strongly positive for S-100 and KBA.62 and negative for cytokeratin. The single metastatic ocular melanoma in the series was negative for KBA-62 but stained positive for KIT in >75% of tumor cells.
Conclusions: MMMs to the liver on FNA samples can be negative for either one or both commonly used melanoma markers. KBA.62 can be an equally effective melanoma marker for MMMs to the liver and may be used in cases that are negative for Mart-1 and HMB-45. KIT expression occurs in approximately 41% of MMMs to the liver, in keeping with previously reported studies.
Category: Cytopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 57, Tuesday Morning


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