Primary Cutaneous Myxofibrosarcoma Mimicking Pleomorphic Hyalinizing Angiectatic Tumor (PHAT): A Potential Diagnostic Pitfall

Abstract

To the Editor: In their recent paper,1 Mitsuhashi et al reported a case of primary cutaneous myxofibrosarcoma (MFS) diagnosed as pleomorphic hyalinizing angiectatic tumor (PHAT) before its recurrence in a more typical pattern of MFS. They conclude that MFS may mimic PHAT in some cases and thus the diagnosis of PHAT should be rendered with extreme caution. We made several similar observations in our institution. In fact, we observed areas resembling those of typical PHAT, ie, thick-walled ecstatic vessels and pleomorphic atypical cells with nuclear pseudoinclusions, low mitotic rate (<1 per 50 high-power fields) and cytoplasmic deposits of hemosiderin in 5 cases of other mesenchymal neoplasms classified as MFS (Figs. 1, 2), high-grade pleomorphic sarcomas and pleomorphic lipoma with prominent vasculature. Atypical features inconsistent with PHAT such as higher mitotic rate (>1 per 50 high-power fields) and/or atypical mitotic figures and/or tumor necrosis and/or areas more typical of other tumor types were observed in each case after extensive sampling and careful examination. Thus, according with Mitsuhashi et al, we think that the diagnostic criteria of PHAT are non specific by themselves and this diagnosis should be rendered only after exclusion of another tumor type by extensive sampling and careful research of atypical features.FIGURE 1.: A, Tumor of the ankle showing areas of typical PHAT with pleomorphic atypical cells around thick-walled ecstatic vessels. B, Pleomorphic nuclei with frequent clear pseudoinclusions (left). No mitotic figure was seen in this area. The tumor cells contained abundant cytoplasmic hemosiderin deposits highlighted with the Prussian-blue stain (right).FIGURE 2.: A, Highly myxoid area (left) adjacent to an area with prominent ecstatic thick-walled vessels reminiscent of PHAT (right). B, Myxofibrosarcoma area with atypical cells within a prominent myxoid matrix with curvilinear vessels.The authors suggested that some cases of PHAT may represent a more aggressive type of soft tissue tumor and may even evolve into a high-grade sarcoma if not completely excised. In fact, Folpe and Weiss reported in their recent publication a case of PHAT that recurred in the form of a high-grade MFS.2 Aggressive local recurrences have also been described in the original paper,3 suggesting an aggressive potential for this type of tumor if not completely excised. The observation of areas resembling PHAT in other malignant mesenchymal neoplasms raises the question of the existence of PHAT as a specific tumor type. To our knowledge, only one cytogenetic study on PHAT by Bridge et al has been to date reported in the form of an abstract.4 They demonstrated cytogenetic abnormalities in 3 of 4 cases of PHAT (cases from the orginal paper3), 2 cases with trisomy 7 and 1 case with 2 supernumerary ring chromosomes constituted of fragments of chromosomes 7, 13, and 16. Interestingly, the presence of such supernumerary ring chromosomes is similar to other low-grade mesenchymal neoplasms capable of dedifferentiation such as certain forms of MFS, well-differentiated liposarcoma, dermatofibrosarcoma protuberans and parosteal osteosarcoma. If this observation is confirmed by further studies, PHAT should be considered as a low-grade neoplasm with a potential for malignant transformation. However, this study demonstrates a cytogenetic heterogeneity in a few available cases raising the question of the classification of PHAT as a single cytogenetically well-defined entity or as a non-specific morphologic feature of other mesenchymal tumors such as MFS. In conclusion, regarding the literature and our additional institutional experience, the diagnostic criteria of PHAT ie, ectatic vessels and pleomorphic atypical cells with no mitotic activity seems to be not specific by themselves and thus the diagnosis of PHAT should be made only after exclusion of other tumor types by extensive sampling and careful research of atypical features. Additional cytogenetic and molecular studies are now needed in addition to clinical and histologic reports to establish whether PHAT constitute a distinct entity or represents a non-specific morphologic feature that can be occasionally seen in other mesenchymal neoplasms. Mathieu Capovilla, MD Philippe Birembaut, MD Laboratoire Pol-Bouin Hôpital Maison-Blanche Reims, France