Procollagen 1 and Melan-A expression in desmoplastic melanomas.Am J Dermatopathol. 2009 Apr;31(2):173-6.
The histopathologic diagnosis of desmoplastic melanoma (DM) is usually based on typical conventional microscopic findings coupled with expression of S100 protein by neoplastic cells. Important differential diagnostic considerations include atypical fibroxanthoma (AFX) and spindle cell squamous carcinoma. Spindle cell squamous cell carcinoma is characterized by positivity for cytokeratin, whereas the diagnosis of AFX has been one of exclusion. Procollagen 1 (PC1) has been identified as a relatively sensitive marker of AFX. In this study, we sought to analyze the expression of PC1, S100 protein, and Melan-A in a series of 37 DMs (27 males and 10 females; ages 36-92 years, mean age 74 years). All lesions displayed a spindle cell morphology with varying degrees of desmoplasia. The neoplastic cells avidly expressed S100 protein in 37 of 37 neoplasms. A complete lack of PC1 expression was noted in 24 of 37 (64.9%). There was a weak PC1 expression by 9 DMs (24.3%) and a moderate expression by 4 DMs (10.8%). Melan-A expression was found in 19 of 37 DMs (51.4%), but in 10 lesions, the expression was only faint and focal. We conclude that PC1 labeling of DM is not uncommon but poses little risk for misdiagnosis, provided the stain is performed as part of panel that includes S100 protein. Melan-A offers little for the diagnosis of DM, as less than a quarter of lesions exhibit a strong reaction with this antibody. It is critical to employ a broad panel of antibodies, including S100 protein, Melan-A, cytokeratin, PC1, and others, in the immunohistochemical evaluation of spindle cell neoplasms of the skin.
Desmoplastic malignant melanoma: a clinicopathologic analysis of 113 cases.Am J Dermatopathol. 2008 Jun;30(3):207-15.
Desmoplastic melanoma (DM) is a rare variant of spindle cell melanoma, which usually develops in sun-damaged skin of elderly patients. Often the lesion is nonpigmented and frequently mistaken for a nonmelanocytic proliferation, which delays diagnosis and treatment and therefore worsens the prognosis. The spindle shape of neoplastic melanocytes, the prominent desmoplasia, and the frequent neurotropism of neoplastic melanocytes are its most characteristic histopathological features. We have studied the clinicopathologic features of 113 cases of DM. The mean age of the patients was 71.1 years; 48% of the patients were males and 52% were females. The neoplasm was located on the head in 72% of the cases. Malignant melanoma was the initial clinical diagnosis in only 27% of the cases. Histopathologically, all lesions appeared as poorly demarcated neoplasms that involved the entire dermis and often extended into the subcutaneous tissue. The neoplasms were composed of ill-defined fascicles of spindle cells. Desmoplasia was defined as the presence of spindle cells associated with a fibrotic stroma. Fifty-one cases (45%) were classified as "pure DM" when the lesion was entirely desmoplastic, and 62 cases (55%) were considered as "combined DM" when a recognizable desmoplastic component was seen in an otherwise conventional malignant melanoma. In 81% of the cases, an atypical intraepidermal melanocytic component (in situ malignant melanoma) was identified, whereas in the remaining 19% of the cases the intraepidermal component was lacking. Seventy-one percent of the cases were histologically amelanotic, 23% showed a small amount of pigment, and only 6% were heavily pigmented. Neural involvement was identified in 40/113 cases (35%), predominantly in the thickest tumors. Lymphoid nodules, found in 42/113 cases (37%), were significantly more frequent in pure DM than in combined DM (53% vs 24%). The null hypothesis of homogeneity of the "pure" and "combined" subgroups should be rejected (P <0.002).>Solar elastosis, with variable intensity, was seen in 82% of the cases.
Mean Breslow thickness was 4.1 mm (4.6/3.7 mm, in the pure/combined subgroups, respectively), median was 4.0 mm (4.0/3.0 mm); Breslow thickness ranged from 0.3 to 11.0 mm, with half of the cases thicker than 4 mm. Only 4% of the cases showed Clark level below IV. The predominant neoplastic cells consisted of spindle-shaped melanocytes in 85% of the cases, whereas the remaining 15% of the cases demonstrated round neoplastic cells forming the main mass of the neoplasm. The mitotic rate of the neoplastic cells was low in 72% of the cases, 23% had an intermediate mitotic rate, and 5% showed a high mitotic rate. On follow-up, 55/113 patients (49%) (with an average of 55 months) demonstrated persistence of the disease. About 4% had local recurrences, 2% of lymph node invasion, 9% systemic metastases, and 12% died from the disease (2 cases of pure DM and 5 cases of combined DM). Although a better prognosis has been postulated for DM when compared with conventional cutaneous malignant melanomas of the same thickness, in most cases, a DM is diagnosed only in established long-standing and thick melanomas. Therefore, dermatologists and dermatopathologists should be more aware of this clinicopathologic variant of cutaneous malignant melanoma.