Melanoma desmoplastic C43.L

Rare variant of malignant melanoma (4% of all primary cutaneous melanomas), which is clinically manifested as malignant amelanotic melanoma in 2/3 of the cases. The desmoplastic melanoma can develop de novo, but can also occur in lentigo-maligna melanoma, acrolentiginous melanoma or in mucosal melanomas.

Desmoplastic melanoma accounts for about 4% of all primary melanomas.

Mainly head and neck (50%), extremities (25%), trunk (20%) especially in the area of light-exposed areas, also in malignant melanomas of the mucous membranes.

Variable clinical picture. Plaque-shaped or nodular, asymptomatic, skin-coloured or reddened, rarely brown-coloured, rough new formation. There may also only be an inconspicuous plate-like induration of the skin. This type of melanoma is often detected late due to its atypical growth (amelanotic tendency) (at initial diagnosis a Breslow index is found in 40% of patients > 4.0 mm, median tumour thickness at initial diagnosis 2.6 mm compared to 0.96 mm in an average melanoma collective (Livestro DP 2006).

The desmoplastic melanoma tends to aggressive, infiltrative growth.

Metastasis: The metastatic tendency of the desmoplastic melanoma is low. The most frequent type of metastasis is locoregional metastasis (about 25%; especially if neurotropism is detected). Less frequent are lymph node metastasis (about 10%) and systemic metastasis (about 20%; correlation with previous local recurrences).

• Fascicular or nodular cell trains of atypical, hyperchromatic, spindle cells, which lie between the fibrotically compressed collagenous fibres. Occasional mitoses. Focal, perivascular lymphohistiocytic infiltrates, fibrosis. Proliferation of atypical melanocytes at the dermoepidermal junction zone, low pigmentation. Desmoplastic melanomas show neurotrophy and follow the course of the dermal nerves (desmoplastic-neutral melanoma).
• Immunohistology: S-100-, HMB-45-, Melan-A- and vimentin-positive; HMB-45 and Melan-A can be in the deep parts or completely negative (!). S-100 is the most reliable marker.

• Clinical signs: Lentigo maligna; hypertrophic scar, spinocellular carcinoma; melanocytic nevus; lymphocytic infiltration of the skin; dermatofibroma; dermatofibrosarcoma protuberans; fibroxanthoma.
• Histological: Dermatofibrosarcoma protuberans (cell-rich, dense dressings of monomorphic tumor associations with chromatin-tight nuclei, expression of CD34); dermal fibrosarcoma (negative for S-100); undifferentiated, desmoplastic-growing spinocellular carcinoma = carcinoma, spinocellular, desmoplastic (expression of cytokeratin).

• Operational:
• Resection of the primary tumour with the aim of R0 resection (according to the general surgical guidelines for malignant melanoma).
• Radiotherapy:
• Good results are achieved with desmoplastic malignant melanoma with postoperative follow-up radiation. This is followed by a significant reduction of the recurrence rate.
• In principle, the S3 guideline recommends postoperative radiotherapy for desmoplastic melanomas that were not resected with sufficient safety margin (safety margin <1cm, or R1/R2) (recommendation level B; evidence level 3b).

Unfavorable due to early deep infiltration of the subcutis and an average tumor thickness(Breslow index) of 4.5-5.7 mm (late diagnosis due to the atypical clinical picture) at diagnosis. A generous surgical procedure with a wide absence of tumour to the side and depth is necessary. Relatively late metastasis tendency; high tendency to local recurrence! The neurotropism of desmoplastic melanoma is another prognostic factor. It is associated with deep tumor thickness, higher mitotic activity, higher recurrence rate and higher tendency to metastasis.

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