Antibodies directed against
alpha-inhibin have been previously reported as staining both sex cord-stromal
neoplasms as well as adrenal cortical
tumors. This relatively restricted immunoreactivity pattern is useful in the assessment of retroperitoneal masses, especially in a setting of limited tissue (e.g., needle biopsy). However, no study to date has evaluated
alpha-inhibin immunoreactivity in
soft-tissue neoplasms, which frequently enter the differential diagnosis of retroperitoneal masses. We investigate the incidence of
alpha-inhibin staining in a variety of
soft-tissue neoplasms by using
formalin-fixed,
paraffin-embedded tissue sections from 282 previously classified
soft-tissue neoplasms with anti-
alpha-inhibin (Serotec, 1:75). A modified
avidin-
biotin complex method was used after heat-induced
epitope retrieval. Cytoplasmic granular staining was considered positive. Of the 282
tumors studied, a total of 8 (2.8%) demonstrated positive staining with anti-
alpha-inhibin antibody. These included 4 of 25
liposarcomas (16%), 2 of 18
angiosarcomas (11%), 1 of 48
lipomas (2.1%), and 1 of 1
rhabdomyoma (100%). Negative staining was noted among
hemangiomas (0/28),
schwannomas (0/32),
leiomyomas (0/16),
fibrosarcomas (0/2),
fibromas (0/11),
dermatofibromas (0/9),
neurofibromas (0/6),
synovial sarcomas (0/15),
rhabdomyosarcomas (0/10), Triton
tumors (0/2), and
malignant fibrous histiocytomas (0/59). We conclude that rare soft-tissue
tumors, especially those exhibiting either lipomatous or vascular differentiation, demonstrate
alpha-inhibin immunoreactivity. These findings re-emphasize the need for a well-construed antibody panel when immunohistochemical methods are employed in the evaluation of
retroperitoneal neoplasms. However, the rarity of
alpha-inhibin expression by
soft-tissue neoplasms provides further support for its overall specificity as a marker of adrenal cortical differentiation in the biopsy evaluation of a retroperitoneal mass.