MSA

(Melanosome specific antigen (HMB-45))
Characteristics
Melanosome specific antigen (MSA) is an incompletely characterized oligosaccharide side chain of a glycoconjugate, 10 kDa, detected by the monoclonal antibody HMB-45 (Human Melanoma, Black). The protein, also designated gp100, encoded by gene gp100-cl, is located in the premelanosomas in stage 1 and 2 and the non-melanised portion in stage 3. MSA is present in immature and activated melanocytes (due to, e.g., inflammation, increased vascularity or underlying tumour), but not in mature, resting melanocytes. There has been reports on HMB-45 reactivity in epithelial cells, this is probably due to contamination of the antibody.
Neoplasms
Malignant melanoma are MSA positive in most cases (60-90%). However, spindle cell and desmoplastic malignant melanoma are MSA negative or only focally positive. MSA is found in varying proportions of benign melanocytic tumours like junction naevus and compound naevus. In these lesions, the epidermal part may be strongly stained while the dermal part is weakly staiend or unstained. Moreover MSA is detected in most caeses of blue naevus, cellular blue naevus, dysplastic naevus, Spitz naevus etc. MSA is also demonstrated in other tumours of melanocytic origin or differentiation (i.e., melanosome producing), such as clear cell sarcoma, proximal type epitheloid sarcoma, pulmonary blastoma, hepatoblastoma, phaeochromocytoma, melanotic neurofibroma and schwannoma and other neural crest derived tumours, as well as in so-called PEComas (perivascular epitheloid cell) derived from modified smooth muscle cells in the so-called tuberous sclerosis complex: angiomyolipoma, lymphangioleiomyoma(-tosis), and pulmonary sugar tumour, and cardiac rhabdomyoma. There are a few reports of aberrant MSA expression in adenocarcinoma. This is probably due to contamination of the antibody.
Application
Being a highly specific marker, MSA has been widely used for the identification of melanocytic differentiation. However, MSA is generally a less sensitive marker than Melan-A and microphthalmia transcription factor (Mitf), particularly in the dermal component of benign melanocytic tumours and in spindle cell melanoma. MSA is useful for the identification of PEComa (together with alpha smooth muscle actin), but also here Melan-A may give a stronger staining.
Controls
It is difficult to identify any normal tissue expressing a consistent level of MSA to be used as a recommendable positive tissue control. Normal resting melanocytes in skin are typically not demonstrated by the mAb clone HMB-45. In order to validate a high sensitivity of the protocol an optimal calibration has to be performed. Tumours with both high and low level MSA expression must be used both during technical calibration of the protocol and as positive tissue controls. In the NordiQC assessments for MSA, blue nevus (run 7, 2003) and angiomyolipoma (run 40, 2014) thus have been superior to malignant melanomas. Using one of these neoplasias, the majority of neoplastic cells must show an at least weak to moderate and distinct granular cytoplasmic staining reaction. Kidney or appendix can be used as negative tissue controls; no staining reaction should be seen in the epithelial cells.
Selected references
Ashfaq R, Weinberg AG, Albores-Saavedra J. Renal angiomyolipoma and HMB-45 reactivity. Cancer 1993, 71(10):3091-97. Baisden BL, Askin FB, Lange JR, Westra WH. HMB-45 immunohistochemical staining of sentinel lymph nodes: a specific method for enhancing detection of micrometastases in patients with melanoma. Am J Surg Pathol 2000, 24(8):1140-46. Blessing K, Grant JJ, Sanders DS, Kennedy MM, Husain A, Coburn P. Small cell malignant melanoma: a variant of naevoid melanoma. Clinicopathological features and histological differential diagnosis. J Clin Pathol 2000, 53(8); 591-5. Bonsib SM. HMB-45 reactivity in renal leiomyomas and leiomyosarcomas. Mod Pathol 1996, 9(6):664-9 Clarkson KS, Sturdgess IC, Molyneux AJ. The usefulness of tyrosinase in the immunohistochemical assessment of melanocytic lesions: a comparison of the novel T311 antibody (anti-tyrosinase) with S-100, HMB45, and A103 (anti-melan-A). J Clin Pathol. 2001 Mar;54(3):196-200. Chan JK, Tsang WY, Pau MY, Tang MC, Pang SW, Fletcher CD. Lymphangiomyomatosis and angiomyolipoma; closely related entities characterized by hamartomatous proliferations of HMB-45-positive smooth muscle. Histopathology 1993. 22(5):445-55. Fetsch JF, Michal M, Miettinen M. Pigmented (melanocytic) neurofibroma: a clinicopathologic and immunohistochemical analysis of 19 lesions from 17 patients. Am J Surg Pathol 2000, 24(3):331-43. Friedman HD, Tatum AH. HMB-45-positive malignant lymphoma. A case report with literaure review of aberrant HMB-45 reactivity. Arch Patol Lab Med 1991, 115(8):826-30 Gown AM et al. Monoclonal antibodies specific for melanocytic tumors distinguish subpopulations of melanocytes. Am J Pathol 1986, 123:195-. Guillou L, Wadden C, Coindre JM, Krausz T, Fletcher CD. ”Proximal-type” epithelioid sarcoma, a distinctive aggressive neoplasm showing rhabdoid features. Clinicopathologic, immunohistochemical and ultrastructural study of a series. Am J Surg Pathol 1997, 21(2):130-46. Heegaard S, Jensen OA, Prause JU. Immunohistochemical diagnosis of malignant melanoma of the conjunctiva and uvea: comparison of the novel antibody against melan-A with S100 protein and HMB-45. Melanoma Res. 2000 Aug;10(4):350-4. Jungbluth AA, Iversen K, Coplan K, Williamson B, Chen YT, Stockert E, Old LJ, Busam KJ. Expression of melanocyte-associated markers gp-100 and Melan-A/MART-1 in angiomyolipomas. An immunohistochemical and rt-PCR analysis. Virchows Arch 1999, 434(5):429-35. Kornstein MJ, Franco AP. Specificity of HMB-45. Arch Pathol Lab Med 1990, 114(5):450. Leong AS-Y, Milos J. An assessment of a melanocyte-specific antibody (HMB-45) and other immunohistochemical markers for malignant melanomas in paraffin-embedded tissues. Am J Surg Pathol 1989, 2:137. Miettinen M, Fernandez M, Franssila K, Gatalica Z, Lasota J, Sarlomo-Rikala M. Microphthalmia transcription factor in the immunohistochemical diagnosis of metastatic melanoma: comparison with four other melanoma markers. Am J Surg Pathol. 2001 Feb;25(2):205-11. Mirecka J, Korabiowska M, Schauer A. Comparative distribution of s-100 protein and antigen HMB-45 in various types of melanomas and naevi. Pol J Pathol 1995, 46(3):167-72 Ordonez N, Ji XL, Hickey RC. Comparison of HMB-45 monoclonal antibody and S-100 protein in the immunohistochemical diagnosis of melanoma. Am J Clin Pathol, 1988; 90(4):385-90. Pea M, Bonetti F, Zamboni G, Martignoni G, Riva M, Colombari R, Mombello A, Bonzanini M, Scarpa A, Ghimenton C et al. Melanocyte-marker HMB-45 is regularly expressed in angiomyolipoma of the kidney. Pathology 1991, 23(3): 185-88. Prasad ML, Jungbluth AA, Iversen K, Huvos AG, Busam KJ. Expression of melanocytic differentiation markers in malignant melanomas of the oral and sinonasal mucosa. Am J Surg Pathol 2001, 25(6):782-7. Sheffield MV, Yee H, Dorvault CC, Weilbaecher KN, Eltoum IA, Siegal GP, Fisher DE, Chhieng DC. Comparison of five antibodies as markers in the diagnosis of melanoma in cytologic preparations. Am J Clin Pathol. 2002 Dec;118(6):930-6. Shidham VB, Qi DY, Acker S, Kampalath B, Chang CC, George V, Komorowski R, Evaluation of micrometastases in sentinel nodes of cutaneous melanoma: higher diagnostic accuracy with Melan-A and MART-1 compared with S-100 and HMB-45. Am J Surg Pathol 2001, 25(8):1039-46. Tazelaar HD, Batts KP, Stigley JR. Primary extrapulmonary sugar tumor (PEST): a report of four cases. Mod Pathol 2001. 14(6):615-22. Xu, X., Chu, A. Y., Pasha, T. L., Elder, D. E., Zhang, P. J. Immunoprofile of MITF, tyrosinase, melan-A, and MAGE-1 in HMB45- negative melanomas. Am J Surg Pathol 2002;26:82-87. Zembowicz A, Granter SR, McKee PH, Mihm MC. Amelanotic cellular blue nevus: a hypopigmented variant of the cellular blue nevus: clinicopathologic analysis of 20 cases. Am J Surg Pathol. 2002 Nov;26(11):1493-500.
11.04.14 - TS/MV/LE