Background: Pilomatrix carcinoma, a malignant variant of pilomatrixoma, is extremely rare. The authors report 20 patients with pilomatrix carcinoma and review the pertinent literature.
Methods: Tumors showing histologic features of pilomatrix carcinoma were selected from the files of the Armed Forces Institute of Pathology. Clinical data of the 20 selected patients were reviewed, and follow-up information was obtained. Sections stained with hematoxylin and eosin were studied in all patients. Special stains were used in selected patients.
Results: Pilomatrix carcinomas were asymptomatic dermal and subcutaneous masses with a predilection for the posterior neck and back. Tumors varied in size, from 1-10 cm (mean, 4.6 cm), and occurred more often in middle-age men, with a male:female ratio of 4:1 (mean age, 45 years). Histologically, pilomatrix carcinomas are characterized by sheets and islands of proliferating atypical basaloid cells with an infiltrating border. Transition to squamous cells, clear cells, areas of necrosis and mitoses often are seen. Keratinization with formation of keratin cysts, shadow cells, and trichohyalin and keratohyalin granules are found in all tumors, in conjunction with calcification and foreign body giant cell reaction, just as are seen in benign pilomatrixoma. Follow-up of 17 patients revealed local recurrence in 10 (59%), with multiple recurrences in 3. One patient had pulmonary metastasis, and one died of extensive local spread of the tumor.
Conclusion: Pilomatrix carcinomas are locally aggressive tumors that have a tendency to recur, especially when they are incompletely excised. Greater anaplasia and deep soft tissue infiltration were associated with a higher incidence of recurrence and death. Wide excision is the preferred treatment. The role of radiation therapy is unclear.