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British Journal of Plastic Surgery (1998), 51,258-259 © 1998 The British Association of Plastic Surgeons BRITISH JOURNAL OF ~ PLASTIC SURGERY CASE REPORT Metastatic malignant melanoma of unknown primary site: a case of a possible primary declaring itself 18 months after the secondaries M. Kumar, R. DeBono and B. C. Sommerlad The St. Andrew's Centre for Plastic Surgery, St. Andrew's Hospital, Billericay, Essex, UK Malignant melanoma is well known for its unpredictable behaviour. Metastatic melanoma occurring without a known primary site is very well documented and dis- cussed in the literature. The incidence of "unknown primary" metastatic malignant melanoma is said to be around 4-5%.~.2 Clinical presentation is very variable, ranging from a palpable mass, e.g. lymphadenopathy, to systemic symptoms and signs, e.g. weight loss? The aetiology of "unknown primary" melanoma remains a mystery. Various explanations have been put forward: the most commonly accepted and well documented one is that of an unapparent cutaneous primary lesion which has undergone spontaneous regression? Upon review of the literature one notes that there has not been a case described of "unknown primary" metastatic melanoma where the possible primary appeared after the secondaries. We hereby describe a case of "unknown primary" melanoma where the possi- ble primary appeared 18 months after the secondaries. Case report A 56-year-old woman presented with a palpable lump in her left axilla which upon excision biopsy and histological examination was found to contain lymph nodes involved with melanoma deposits. No primary could be identified at that time. She subsequently underwent a left axillary lymph node clearance. Approximately 18 months after the first operation she presented with a fusiform swelling on the pulp of her left thumb (Fig. 1). The swelling was firm in consistency and was associated with some numbness of the pulp of the thumb distal to it. It was explored surgically using magnification, and macroscopically looked like a vascular malformation involving the radial digital artery which seemed to be thrombosed. The swelling was excised and submitted for histological examination. Histological examination revealed that the lesion was a highly malignant tumour showing haemorrhagic necrosis and was deemed to be almost cer- tainly a melanoma. Discussion Malignant melanoma is a perplexing problem due to its capricious behaviour. Melanoma lymph node metastasis without an identifiable cutaneous primary 258 Fig. 1 Figure l--Fusiform swelling on pulp of left thumb. site is a relatively unusual occurrence. Melanoma cells can possibly arise de novo in the lymph node parenchyma? Alternatively, ectopic benign naevus cells within the lymph node may undergo malignant change? However the most widely accepted hypothesis is that of spontaneous regression of the primary cutaneous lesion, possibly as a result of a changing tumour-host immune response. There have been vari- ous cases where patients with unknown primary metastatic melanoma gave a history of a cutaneous lesion which has regressed. 4 There are three possibilities by which one could explain the natural history of the melanoma in the patient described in this case report: 1. The axillary lymph node melanoma and the thumb melanoma could have been two com- pletely unrelated tumours each arising de novo. 2. The thumb lesion might have been present but unnoticed at the time of presentation with the axillary lymph node metastasis, after which it regressed or remained microscopic only to declare itself later. 3. The lesion in the thumb could have arisen as a satellite of a primary axillary lymph node melanoma.
