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This is the first report of malignant melanoma arising from sebaceous nevus (SN) of the scalp, although it has been known that various benign and malignant neoplasms may develop in association with SN. After the excisional biopsy for SN with 5 mm free margin, pathological examination revealed the coexistence of nodular melanoma invading to the reticular dermis (IV level of Clark) for a maximal depth of 4 mm. After resection with another 20 mm free margin, there has been no evidence of local recurrence or distant metastasis for nine years.
We report a case of malignant melanoma in a SN of the scalp. To our knowledge, malignant melanoma arising in a SN has not been described before.
1. Case report
A 47-year-old Japanese woman had had a hairless yellowish plaque on her back scalp from birth. A black nodular lesion appeared on the SN in 1992. Physical examination in 1993 revealed a yellowish mass, 8×20 mm in size, with a black lesion, 6×7 mm, which we suspected clinically to be a basal cell carcinoma (BCC) in SN (Fig. 1) . The regional lymph nodes were not involved. The lesion was excised with 5 mm border of normal scalp, including the epicranial aponeurosis, and closed simply. The histopathological diagnosis was nodular malignant melanoma (NM) in SN with invasion of the reticular dermis (Clark IV level), for a maximal depth of 4 mm (Fig. 2) . There was one mitotic figure per 10 high power fields and the cells were large spindle- or polygonal-shaped with prominent nucleoli.
Fig. 1Yellowish verrucous and nodular mass, 8×20 mm2 in size, with black and nodular lesion, 6×7 mm, on the scalp.
Fig. 2Histologic examination demonstrating malignant melanoma arising from preexisting sebaceous nevus. Nevus tissue was deviated by nodular melanoma, which has typical histopathological features of malignant melanoma. Hematoxylin and eosin stain. Original magnification × 15 (left), × 100 (right).
Surrounding normal skin was widely resected, with a 2.0 cm margin around the previous scar including the epicranial aponeurosis. The area was then covered with meshed split thickness skin graft with pathological confirmation of disease-free margin. One cycle of neoadjuvant and two cycles of adjuvant combination chemotherapy with dacarbazine (DTIC), nimustine hydrochloride (ACNU), vincristine (VCR) and interferon beta were performed. The patient has had no evidence of local recurrence or distant metastasis and is disease free after nine years of follow-up.
2. Discussion
All constituents of human skin are derived from either ectoderm or mesoderm. The epithelial structures (epidermis, pilo-sebaceous-apocrine unit, eccrine unit and nails) are ectodermal derivatives. Nerves and melanocytes emanate from neuroectoderm and neural crest. Mesenchymal structures (collagen, reticulum, and elastic fibers, blood vessels, muscles, and fat), originate from mesoderm.
representing an organizational or embryogenetic defect resulting in an abnormal mixture of tissue of varying types. A variety of tumors arising in SN have been reported, originating from ectodermal or, less often, mesodermal tissues.
where they divided these secondary tumors into six categories according to embryonic aspects. This is the first report that melanocytes, dendritic cells, from neural crest cells of ectodermal derivation had malignant changes in SN.
Table 1Benign and Malignant Tumors Reported in Organoid Nevi
In 1962, Michalowski suggested that SN should be considered a premalignant lesion after he noted 34 carcinomas arising out of total of 160 cases of SN (22%).
have been reported. We would like to include a case of malignant melanoma in this category.
However, the malignant change of melanocytes in SN could conceivably occur by one of two different mechanisms: it is possible that this change occurs spontaneously in melanocytes in SN; alternatively the change may occur under the induction of SN. The mechanism by which this abnormal induction occurs is not known. Ackerman suggests that most malignant melanoma in situ develop de novo, but many surely develop in preexisting melanocytic nevi.
Considering his suggestion, we speculate that malignant change of melanocytes occurs within melanocytes of SN without induction of SN.
On the basis of our own experience and reviews of the literature, it must be stressed that local excision should be carried out early in the patient's life, preferable before puberty, while the lesions are small in size and the likelihood of malignant degeneration is small.
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