Comparison of oncostatin M expression in keratoacanthoma and squamous cellcarcinoma

Oncostatin M (OSM) is a 28-kDa glycoprotein, produced by stimulated macroph ages and T lymphocytes, that inhibits the proliferation and induces differe ntiation of a number of different cell lines derived from solid tumors. To determine whether keratoacanthoma (KA) is unique or a variant of squamous c ell carcinoma (SCC), we compared the immunohistochemical expression of OSM in the tumor cells and peri- and intratumoral macrophages of 21 mature KAs, 7 regressing KAs, and 27 SCCs. An inverse correlation tvas identified betw een OSM tumor labeling and the density of OSM-labeled tumor-associated macr ophages for KAs (r = -.4; P =.09). OSM tumor expression was significantly m ore frequent and more intense in KAs than in SCCs (95% versus 63%; P <.01). In contrast, the density of OSM-labeled macrophages was significantly high er in SCCs compared with mature KAs (7/3 high power fields versus 4/3 high power fields; P = .02). These OSM-positive macrophages were predominantly l ocated at the advancing, infiltrative margins of both neoplasms. Regressing KAs demonstrated a decreased level of OSM tumor expression compared with m ature KAs (53% versus 95%; P =.001), but there was no difference in density of OSM-labeled macrophages, Both the above differences and the overlapping patterns of OSM expression suggest that KAs are a variant of SCC where OSM , possibly as an autocrine factor, may mediate KA's overwhelming but not ab solute tendency to involute.