Other Malignant Neoplasms

Histologically, the tumour consists of sheets of plasma cells that vary in differentiation from well- to poorly differentiated. They may contain Russell bodies or grape-like inclusions of retained immunoglobulin (Mott cells), which are also found in reactive plasma cells and do not help in establishing the diagnosis of plasmacy-toma [142].

Well-differentiated plasmacytoma cannot be distinguished morphologically from reactive (polyclonal) proliferation of plasma cells. Therefore, the monoclonality of plasma cells must be proven, which is best achieved by demonstrating the cytoplasmic immunoglobulin heavy and/or light chain restriction. Besides immunohisto-chemistry, non-isotopic paraffin section in situ hybridisation is useful in the assessment of clonality for kappa or lambda light chain mRNA [389].

Poorly differentiated plasmacytoma must be differentiated from other lymphoid neoplasms and from other malignant tumours, such as malignant melanoma and carcinoma. This is achieved by appropriate immunohis-tochemical analysis; plasmacytoma, in contrast to lymphoma, does not express CD45 and immature B- and T-cell markers [351]. It also does not express antigens characteristic of malignant melanoma (i.e. S-100 protein, HMB-45 and melan-A), carcinoma (cytokeratins) and neuroendocrine neoplasms (i.e. synaptophysin, chromogranin).

Plasmacytoma is radiosensitive and complete eradication by radiation and/or surgery is potentially curative [183, 269, 270, 303, 378]. The prognosis is favourable, although the development of a plasma cell myeloma may occur in 15% of patients with extraosseous plas-macytoma [142].

ICD-O:8720/3

Primary malignant melanoma (MM) of the larynx is extremely rare; less than 60 cases have been described in the literature. They represent 3.6 to 7.4% of all mucosal melanomas of the head and neck [6, 185, 212, 379].

Primary laryngeal MM is more common in men, mostly in the 6th and 7th decades. It occurs primarily in the supraglottic region and less often in the glottic region, but it has not yet been described in the subglottis. The symptoms vary according to the site of involvement and generally occur over a short period of time [379].

Macroscopically, it may present as a polypoid, exophytic, nodular, sessile, or pedunculated lesion, with or without surface ulceration, varying in colour from black or brown, to tan-grey or white.

Microscopically, primary laryngeal MM is indistinguishable from MM of the skin and other mucous membranes. It may be composed of epithelioid cells, spindle cells, or both. Nuclear and cellular pleomorphism, nu clear pseudoinclusions, mitoses and necroses are usually prominent.

The diagnosis is based on histological examination, together with special stainings for melanin, such as Fon-tana-Masson, and immunohistochemistry.

The differential diagnosis must always include the possibility of a metastatic MM because in the larynx, metastatic MM is considerably more common than primary MM [153]. Histologic features that favour the diagnosis of primary MM are junctional activity and/or an in situ component. However, as normal melanocytes are also normally present in the subepithelial compartment, junctional changes are not required for the diagnosis of primary MM [379].

Apart from metastatic MM, the differential diagnosis includes carcinoma (especially spindle cell carcinoma), sarcoma and lymphoma. Positive staining for well-known MM markers, such as S-100 protein, HMB-45, melan-A and vimentin, and negative staining for CD45, B- and T-cell markers, as well as markers of epithelial differentiation (cytokeratins, epithelial membrane antigen) is diagnostic for MM.

The treatment of choice is complete surgical excision. The prognosis of primary laryngeal MM is poor, similar to primary mucosal malignant melanoma in general, with an average survival of less than 3.5 years [260, 379].

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