[1826] Malignant Mesothelioma Expresses Melan-A (A-103), a Possible Diagnostic Pitfall.

Maryam Zenali, Michael T Deavers, Neda Kalhor, Victor G Prieto. MD-Anderson Cancer Center, Houston, TX

Background: Malignant mesothelioma, with its numerous morphologic subtypes, may well enter into the differential diagnosis of melanoma, clear cell (sugar) tumor, adrenal cortical, and sex cord stromal tumors. The immunohistochemical patterns of expression of these tumors partly overlap since even keratins can be expressed in all of them. Expression of melanocytic marker Melan-A (A103 clone) has also been documented in adrenal cortical neoplasms, sugar tumor, and sex-cord stromal tumors. However, to the best of our knowledge, expression of Melan-A (A103) has not been documented in malignant mesothelioma. This study analyzes the possible expression of A103 in mesothelioma and compares it with other melanocytic markers.
Design: 12 specimens with the diagnosis of malignant mesothelioma (epithelioid type) were collected from the files. These were from 2 females and 6 males (in 2 cases more than one metastatic site was evaluated), ranging from 40 to 73 years of age. Sites of disease included: lung/pleura, mediastinum, small bowel/mesentery, peritoneum, and uterus/ovaries. 5-micron sections of paraffin embedded tissue were utilized for immunohistochemical analysis with anti-MART-1 (clone Ab3; Thermo), Melan-A (clone A103; Labvision), and anti-Tyrosinase (clone T311; Leica).
Results: Table 1 summarizes IHC findings. All cases (12/12) showed strong positive labeling for Melan-A (A103); 4 cases had at least focal expression of tyrosinase. MART1 was negative in all cases examined.

case #MART-1Melan-A (A 103)Tyrosinase
104+Rare cells +
204+Rare cells +
704+Rare cells +
10N/P3+Rare cells +
12N/P3+Rare cells +
Grading: 2-10%=1+; 10-40%=2+; 40-70%=3+; 70-100%=4+; N/P: not performed

Conclusions: Expression of Melan-A (A103) or tyrosinase can be seen in epithelioid mesothelioma. These findings warrant caution in the diagnostic use of Melan-A (A103) or tyrosinase in differentiating malignant mesothelioma form metastatic melanoma, clear cell tumor, adrenal cortical, and sex cord stromal tumors.
Category: Pulmonary

Tuesday, March 1, 2011 2:00 PM

Platform Session: Section F, Tuesday Afternoon


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