Ossifying fibromyxoid tumor: a clinicopathologic analysis of 26 subcutaneous tumors with emphasis on differential diagnosis and prognostic factors.

INTRODUCTION

Ossifying fibromyxoid tumor (OFMT) is rare and may present diagnostic difficulty. We describe 26 subcutaneous examples of OFMT emphasizing differential diagnosis and prognostic features.

METHODS

Histopathology and follow-up data from archival/consultation cases were reviewed. Prognostic features were assessed according to proposed criteria.

RESULTS

Patients (16 female, 10 male) ranged from 26 to 88 years (median 54). The tumors (median 2.3 cm, range 0.8-8.5) involved lower limb (11), trunk (7), head/neck (4), or arm (4). All showed combinations of corded, nested and trabecular patterns in a fibromyxoid stroma. Out of 26 cases 13 had peripheral ossification. Sixteen of 22 cases showed S100 protein expression. Nuclear grade was low (14); intermediate (8) and high (4) while cellularity was low (14); moderate (7) and high (5), with overall good interobserver agreement. Median mitotic rate was 3/50HPF (0-61). Five met criteria for malignant OFMT showing high nuclear grade or high cellularity and mitotic rate >2/50HPF or both. Thirteen OFMTs were atypical. Follow-up (16/26, median 45.5 months, range 8-108) showed that patients with typical OFMT (3) and atypical OFMT (9) remained disease-free. Three malignant examples of OFMT recurred and one metastasized to the lung. No deaths were recorded.

CONCLUSIONS

Our results validate proposed prognostic classification of OFMT. Dermatopathologists should be aware of this unusual superficial tumor given its potentially aggressive behavior.