Pleomorphic hyalinizing angiectatic tumor: analysis of 41 cases supporting evolution from a distinctive precursor lesion.

The pleomorphic hyalinizing angiectatic tumor (PHAT) is a rare, low-grade neoplasm that features atypical stromal cells containing hemosiderin, partially thrombosed ectatic vessels with circumferential hyalinization, and a variable inflammatory infiltrate. Over the years, we have occasionally observed a monomorphic partially myxoid spindle cell component (provisionally termed "early PHAT") co-existing with classic PHAT. In some instances, this monomorphic lesion occurs by itself, suggesting an early stage in the evolution of PHAT. To explore this hypothesis and to better define the long-term behavior of PHAT, we have reviewed our experience with these lesions. Forty-one cases were identified from consultation files. They occurred chiefly in adults (median 51 years, range 10-79 years) of either sex (23 female, 18 male), ranged from 0.3 to 19.7 cm (median 5.6 cm), and involved the subcutis of the ankle/foot (N = 15), leg (N = 10), thigh (N = 6), and other sites. Thirteen tumors had been present for more than 1 year prior to biopsy. Fifteen tumors consisted entirely of typical PHAT. Twelve cases conformed to "early PHAT," lacked fully developed features of PHAT, and showed instead short fascicles of hemosiderin-stippled spindled cells that infiltrated fat and surrounded congeries of small, damaged vessels. With close scrutiny, all contained rare pleomorphic cells with intranuclear pseudo-inclusions, as seen in typical PHAT. Fourteen cases contained both classic and early PHAT, in variable proportions. Follow-up was available in 18 patients (mean 84 months, median 52 months; range 13-420 months). Six of 18 patients developed recurrences, 1 with classic PHAT, 1 with mixed early-classic PHAT, and 4 with early PHAT. Following resection, 16 are disease free and 2 have persistent disease. None has developed metastasis. Based on the histologic overlap between early and classic PHAT, the presence of early PHAT at the periphery of classic PHAT, and the admixture of both patterns within the same tumor, we conclude that early PHAT represents a precursor lesion for PHAT. It appears essentially identical to the lesion termed "hemosiderotic fibrohistiocytic lipomatous lesion," supporting the notion that the latter is a neoplastic rather than a reactive lesion. PHAT should be considered mesenchymal tumors of intermediate malignancy, given their high rate of (sometimes aggressive) local recurrence.