Responding to “Primary Cutaneous Myxofibrosarcoma Mimicking Pleomorphic Hyalinizing Angiectatic Tumor (PHAT): A Potential Diagnostic Pitfall”
We completely agree with the conclusions of Drs Capovilla and Birembaut, who found areas mimicking pleomorphic hyalinizing angiectatic tumor (PHAT) in 5 cases of other malignant soft tissue tumors. They point out that the “characteristic” histologic findings of PHAT, namely pleomorphic spindled and rounded cells with occasional nuclear pseudoinclusions, prominent thick-walled, hyalinized vessels, and a low mitotic rate, may be found in malignant soft tissue tumors. Their cases clearly emphasize the point that PHAT is a “high-risk” diagnosis that should only be made with great care and trepidation, and that at least some cases diagnosed as “PHAT” may represent incompletely sampled sarcomas.
Although it has not been emphasized in the literature, several eminent soft tissue pathologists have stated personally that they have seen cases of sarcomas that have either mimicked PHAT or evolved from lesions diagnosed as PHAT. On the basis of these observations, the 5 cases reported above by Capovilla and Birembaut, as well as our case1 and the similar one reported by Folpe and Weiss (high-grade myxofibrosarcoma recurrence in a PHAT),2 we believe that it is possible that PHAT may merely represent a histologic pattern and not a true clinicopathologic entity. As pointed out by Capovilla and Birembaut, extensive cytogenetic and molecular studies of PHAT have not been performed to date, and the preliminary cytogenetics results do not seem to indicate a specific, recurring chromosomal alteration.3 Further cytogenetic and molecular studies are clearly required to clarify this issue.
Whereas it may be argued that PHAT is a distinctive clinicopathologic entity based on its generally low-grade behavior and lack of reported metastases, this may simply reflect the requirement of a low mitotic rate for the diagnosis of PHAT. Cases with all of the other histologic features of PHAT and a higher mitotic rate are likely simply diagnosed as sarcomas. Analogous to the current thinking regarding malignant fibrous histiocytoma, PHAT may eventually come to be regarded as a morphologic pattern that may be found in many soft tissue tumors. At the very least, PHAT should be considered a provisional entity, and should clearly be classified as a tumor of intermediate malignant potential, and not as a benign tumor, as the current WHO classification designates it.