Ganglionic melanoma without cutaneous localization: primitive, or metastasis?

Melanoma with unknown primary site, described for the first time in 1952 [1], is defined as histologically confirmed subcutaneous, lymph nodal or visceral metastatic melanoma with no evidence of primary lesion.Melanoma is developed from melanocytes, Although most develop on sunlight-exposed areas, this disease can also developon other areas. Melanomas of the eye, ear, vaginale epthelium, meninges are well documented but rare. They account for less than 10% of all melanomas [2]. we report a patient with lymphadenopathy melanoma with no known primary site.


INTRODUCTION
Melanoma with unknown primary site, described for the first time in 1952 [1], is defined as histologically confirmed subcutaneous, lymph nodal or visceral metastatic melanoma with no evidence of primary lesion.Melanoma is developed from melanocytes, Although most develop on sunlight-exposed areas, this disease can also developon other areas. Melanomas of the eye, ear, vaginale epthelium, meninges are well documented but rare. They account for less than 10% of all melanomas [2]. we report a patient with lymphadenopathy melanoma with no known primary site.

CASE REPORT
A 73-year-old patient, without any notable pathological history, consulted after discovery of an asymptomatic inguinal mass, appeared over 1 month, without any other signs associated. The examination of the ganglion air found left inguinal lymphadenopathy, 3 cm in size, without inflammatory signs. Dermatologic examination revealed achromic macules on the back, the legs, and genital, with a body surface area of 3% ( Fig. 1), and with contrast enhancement in "Wood's light". And revealed three dermal nevus not suspect clinically, seat at the neck and back. The rest of somatic examination was normal, with a general state preserved. Ultrasonography of the ganglionic areas found hypoechogenic left inguinal adenopathies of 25mm for the largest central necrosis and anarchic vascularization. The biopsy of adenopathy was made, of which histology and immunohistochemistry (HMB 45+, S100 +, Melan A +), was in favor of ganglionic melanoma. The mutaton anti-BRAF and C-KIT was negative.
The search for the primitive by the ophthalmologic examination, cervico-vaginal smear, ano-rectocolonoscopy, as well as a cerebral CT did not bring any element in favor of melanoma. The cervical-thoracicabdominopelvic CT showed no other metastatic locations. The biological assessment was normal. Then a PET scanner showed a subcutaneous nodule opposite the anterior surface of the tibial plateau weakly hyper-metabolic (SUVmax0,7) An excision of this lesion did not objectify a cutaneous melanoma.
The patient was treated by inguinal lymphadenopathy surgery, and radiotherapy (30gr fraction over 5 sessions) (Fig. 2). Four months after treatment, the cervicalthoracic-abdominopelvic CT showed the appearance of others lymphadenopathy internal iliac with central necrosis. then the patient was treated by chemotherapy with size stabilization of the lymphadenopathy on the control scanner, after 6 months of follow-up, without relapse.

DISCUSSION
Melanoma of lymph nodes with unknown primary site is a rare phenomenon with an incidence of 3.2% [3]. The extra-cutaneous melanoma can come from the uvea, leptomening, mucous membranes and from anywhere in the digestive tract. including gall bladder. It occurs at any age but especially the patients of fourth and fifth decades. It is twice as common in humans. The diagnosis of certainty is histological, confirmed by the Fontana-Masson staining, and the immunohistochemistry (S100, HMB 45). The ganglionic melanoma suggests more a metastatic cutaneous-mucosal primitive, with a complete regression, than a lymph node primitive, seen absence of melanocytes at the ganglion level, and especially if the patient has a vitiligo-like leukoderma associate, as the case of our patient [4]. Melanoma regression is rare, with an incidence of 0.22% to 0.27%. it can be partial in 46%, or complete in 10% of cases, sometimes rapidly. This regression potentially occurs via a tumor specific natural cytolytic T cell response, which explains the vitiliginous response [5]. Although the cause of vitiligolike leukoderma is still unclear, in most situations, but all know that it is an autoimmune disease in which melanocytes are destroyed by antigen-specific T cells. The association vitiligo-like leukoderma and melanoma is described in the literature with an incidence of 2.8%, this association is explained by the fact that melanoma shares several antigens with normal melanocytes including Melan-A/MART-1, tyrosinase and gp100, which leads to a cross-immune reaction [6,7].
The extension assessment is systematic in the melanoma but when normal with a nodal ganglionnaire a systematic pet scanner can be discussed because it this paraclinical "modern" gives a good sensitivity and specificity [8]. The pet scanner of our patient revealed a pre-tibial hypersensitivity whose histology was not specific, but it does not eliminate the regression of melanoma, especially since the lesion sits on the same limb of the lymadenopathy.

CONCLUSION
our case cited here support the hypothesis that lymph node melanoma without obvious primitive suggests a high probability of metastatic melanoma with complete regression, especially if the patient has a vitiliginous immune response.

Consent
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