Microcystic adnexal carcinoma of the skin: the role of adjuvant radiotherapy.

INTRODUCTION: Microcystic adnexal carcinoma (MAC) is a rare cutaneous tumour where the role of radiotherapy remains undefined. We contrast our institutional experience with current literature, define the local control rate and suggest a role for adjuvant radiotherapy in the treatment of this cancer.

METHODS: From 1992-2008, a retrospective review was undertaken for MAC treated with curative intent involving surgery and adjuvant radiotherapy at the Royal Brisbane Hospital and Mater Hospital Brisbane. Clinical, pathologic and treatment details as well as patterns of recurrence were analysed.

RESULTS: Fourteen cases of MAC received local excision and adjuvant radiotherapy. The median age was 71 years old, with nine of the cases in men. All cases occurred in the head and neck region with mean tumour size of 20.5 mm and mean depth of invasion of 9.9 mm. Peri-neural invasion occurred in 56% of cases and 69% had positive surgical margins. Various adjuvant radiotherapy schedules were used to treat the primary site resulting in a crude local control rate of 93%. Primary and nodal relapses were subsequently salvaged with further treatment.

CONCLUSION: While Mohs micrographic surgery may be considered the gold standard, wide local excision and adjuvant radiotherapy offers comparable control rates. Doses of 50 Gy or greater should be prescribed with generous margins (3-5 cm) owing to its tendency for peri-neural and deep invasion. There was no evidence that radiotherapy can cause aggressive transformation of the tumour. The role for definitive radiotherapy remains uncertain.