6.11.09

Desmoplastic melanoma, a common missed diagnosis.

Introduction:

Although desmoplastic melanoma represents less than 2 percent of all melanomas, it's frequently misdiagnosed, due to a lack of distinctive clinical presentation features. Histologic diagnosis is rarely straightforward either.



Patients are often middle age-to-elderly and present with the tumor most often on the head and neck region. The lesion may resemble a scar as it is often a hard nodule or plaque.
Pigmentation is variable but often absent. The tumor has ill-defined margins and is very infiltrative, making local control difficult. Sentinel lymph node excision is routinely performed but rarely positive.

Histology :
The histology can also masquerade as a scar . The epidermis is often atrophic and may or may not have a precursor (in situ) lesion. Characteristically, the tumor is in the dermis as spindled melanocytes resembling fibroblasts.Often, there is an edematous or desmoplastic stroma with
scattered lymphoid aggregates. Perineural invasion is common.In about one third of the lesions, there are foci of epithelioid or conventional melanoma.

S-100 and HMB45 immunohistochemical stains can help differentiate tumor from scar.
At low power, there is a fibrotic lesion in the dermis with scattered lymphoid aggregates.


The lesion is paucicellular, but there is cellular atypia .


Reporting of the histologic subtype of melanoma is common practice, but it is unclear what impact, if any, it has on management decisions. One possible exception is desmoplastic melanoma, a distinct subtype with a unique biologic behavior. It is now recognized that desmoplastic melanomas present with greater tumor thickness (Breslow level) than their conventional counterparts but fail to demonstrate a corresponding higher sentinel lymph node involvement or higher mortality.

Some authors have further subdivided desmoplastic melanomas into "pure" and "mixed" forms. Pure (primarily fibrotic) and mixed varieties, which include features common to conventional melanoma and desmoplastic areas. As per these recent studies only 1% of pure desmoplastic melanomas metastasized to regional lymph nodes compared to 10% with mixed histology.

References:
1. Attis MG, Burchette JL, Selim MA, et al. Differential expression of N-cadherin distinguishes a subset metastasizing desmoplastic melanoma.
2. Davison JM, Rosenbaum E, Barrett TL, et al. Absence of V599E BRAF mutations in desmoplastic melanomas. Cancer. 2005 103:788.
3. Hawkins WG, Busam KJ, Ben-Porat L, et al. Desmoplastic melanoma:a pathologically and clinically distinct form of melanoma. Ann Surg Oncol. 2005 12:207.

4 comments:

Anshu said...

Dear Sir,
an enlightening talk as always. wht cud be the features tht shud make u suspect this diagnosis??
Thanks

Dr.Prashant A.Jani M.D.FRCPC said...

A useful rule is: Actinic damaged skin + scar or desmoplasia = rule out desmoplastic melanoma
This often requires immunohistochemical stains for S100 protein; HMB45 has a low sensitivity for desmoplastic melanoma and is not useful.

Anshu said...

Thanks. wil always kp this in mind

Anonymous said...

The case study is very educative for a pathologist like us ,working in a cancer centre with very limited service for the patients.
Thank you very much
Srijana

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Interesting Case

Clinical History:

53 years male,History of hypertension and tachycardia,MRI abdomen:-Left adrenal mass:- size 5.8 cm Right renal mass:- size-3.0cm Microscopic examination of the renal mass showed vascular tumor with diffuse sheets of clear cells having Fuhrman grade III nuclei. There was no evidence of necrosis within the tumor. There was no evidence of extraparenchymal invasion.
Gross examination of the left adrenal gland revealed cortically centered, solid and multinodular mass measuring 6.5 x 6.0 x 5.0 cm and weighing 122 grams. The tumor was encapsulated but showed evidence of extraparenchymal penetration. The tumor had golden brown cut surface with areas of hemorrhage and necrosis. The partial nephrectomy showed 3.0cm x 3.0cm x 3.0 cm yellow solid mass which did not invade into the perinephric adipose tissue.
Microscopically, the adrenal mass had predominant diffuse sheets and focal trabecular arrangements. The former pattern was present in about third of tumor. The cells had clear cytoplasm and round to ovoid nuclei with conspicuous nucleoli. Mitotic rate was 9/50 HPF and included atypical forms. Gross necrosis and capsular invasion were documented microscopically. There was no evidence of lymphovascular invasion. Considering the above mentioned features, a Weiss histopathologic score2 of 7/9 was applied.



Discussion:

The differential diagnosis included Renal Cell Carcinoma (RCC) with contralateral adrenal metastasis, Adrenocortical carcinoma (ACC) with contralateral renal metastasis, synchronous RCC and ACC or synchronous RCC and adrenocortical adenoma. A panel of immunohistochemical stains was performed to sort out the diagnosis. Adrenal tumor demonstrated strong Vimentin positivity and is negative for CK7, CK20, E1/AE3, EMA, Synaptophysin and S100.Renal cell carcinoma was positive for CK7, AE1/AE3, EMA (weak) and Vimentin. It was negative for CK20, Synaptophysin and S100. The difference of immunoprofile between the two tumors documented that they originated from two different primaries.

Final Diagnosis:

The diagnosis of synchronous RCC and ACC rather than metastasis influences the prognosis.

Prognosis:

The longest disease free interval after removal of contralateral adrenal metastasis was 12.1 years8 and the longest crude survival was 14.3 years. In contrast non metastazing RCC has an excellent prognosis if no metastasis developed.