SM5-1: a new monoclonal antibody which is highly sensitive and specific for melanocytic lesions

Abstract

Antibodies such as HMB-45 and anti-S100 protein have been widely used as markers of malignant melanoma despite evidence that HMB-45 has a sensitivity of only 67-93% and S100 is nonspecific for melanoma. Using a subtractive immunization protocol in a mouse model of human melanoma, we have generated several monoclonal antibodies with putative specificity for melanoma. After initial screenings, the antibody SM5-1 was chosen because of its intriguing reactivity with melanocytic tumors in both frozen and paraffin sections. The immunohistochemical staining of SM5-1 was studied in paraffin-embedded specimens of 401 melanomas (n = 401; 250 primary melanomas, 151 metastases), melanocytic nevi of the skin (n = 16), nonmelanocytic neoplasms (n = 84). The results were compared with HMB-45 and anti-S100 staining. All antibodies reacted with nevi and 97-99% with primary melanomas. Whereas both SM5-1 and anti-S100 stained 96% (146/151) of melanoma metastases, HMB-45 correctly identified only 83% (126/151). All HMB-45-negative metastases were positive for SM5-1. Whereas neither SM5-1 nor HMB-45 stained any of 84 specimens from 40 different nonmelanocytic neoplasms, anti-S100 was positive in 21/84 (25%). While the staining pattern of SM5-1 was mostly homogeneous, small tumor areas in some metastases remained unstained. Staining with SM5-1 was also observed in perivascular dendritic cells, in plasma cells, some myofibroblasts and the secretion of eccrine sweat glands. Nonactivated epidermal melanocytes, keratinocytes, endothelial cells, smooth muscle cells and peripheral nerves were all negative for SM5-1. These results suggest that SM5-1 is highly specific, as well as sensitive, for melanocytic lesions and is useful in the immunohistochemical evaluation of melanoma.

Immunohistochemical characteristics of melanoma

“…10 The specificity of S100 is reported to be 75-87%. 7,11,12 More specific immunohistochemical markers including markers specific for non-melanocytic lesions should be used in parallel with S100 to reliably distinguish melanoma from other S100 positive malignancies. (Tables 1 and 2) HMB45, a marker of the cytoplasmic premelanosomal glycoprotein gp100, was one of the first melanoma Ôspecific' markers discovered.…”

“…5,11 The reported sensitivity of HMB45 for melanoma ranges from 69% to 93%, 5,6,[11][12][13][14][15][16][17] and expression is maximal in primary melanoma specimens (77-100%) and less in metastases (58-83%). 6,[11][12][13][14][15][16][17] Staining may be patchy, and melanoma cells are less diffusely positive than with other markers. 11,14,15,17 There may be strong staining with HMB45 in the epidermal component of a primary melanomas with gradually weaker staining in the deeper vertical growth phase.…”

“…5,6,14 ( Figure 1) There is some dispute as to whether HMB45 is less sensitive in amelanotic melanomas. 5,11 HMB45 is very specific for melanomas and has been reported to be absent from nonmelanocytic tumors by Wick et 7,11,12,13 However, HMB45 is expressed in PEComas (i.e. angiomyolipomas, lymphangiomyomatosis and pulmonary Ôsugar' tumors), sweat gland tumors, meningeal melanocytomas, clear cell sarcoma of the tendons and aponeuroses, some ovarian steroid cell tumors and some breast cancers as well as renal cell carcinomas with a t(6,11)(p21;q12) translocation.…”

“…31,32 Both clones also stain PEComas and can Table 1. Antibodies useful in the diagnosis of epithelioid, pleomorphic and metastatic melanomas -positive markers Marker Sensitivity/specificity Also seen in Comment S100 Sensitivity -97-100%, specificity 75-87% [3][4][5][6][7]11,12 Numerous tumors including but not limited to those derived from nerve sheath cells, myoepithelial cells, adipocytes, chondrocytes, Langerhans cells 4,8 Nuclear and cytoplasmic stain. [3][4][5][6][7] Most sensitive marker for spindle cell/ desmoplastic melanomas.…”

“…[3][4][5][6][7] Most sensitive marker for spindle cell/ desmoplastic melanomas. 11,[14][15][16]30,31,33,34,[36][37][38]42,43 HMB45 Sensitivity -69-93% (77-100% in primary melanomas, 56-83% in metastatic melanomas) 5,6,[11][12][13][14][15][16][17] PEComas (angiomyolipomas, lymphangiomyomatosis, pulmonary Ôsugar' tumors), meningeal melanocytomas, clear cell sarcoma of the tendons and aponeurosis, some ovarian steroid cell tumors sweat gland tumors, some breast cancers, renal cell carcinoma with a t(6,11)(p21;q12) translocation 8,14,[18][19][20][21][22][23][24][25] Cytoplasmic stain. Decreased sensitivity in metastatic melanoma.…”