By Gary M. White, MD
A large MAC on the forehead.
The microcytic adnexal carcinoma (MAC) is a rare, malignant tumor with follicular and eccrine differentiation that tends to occur on the face.
A slow-growing, indurated plaque on the upper lip, nasolabial area or elsewhere on the face is characteristic. Occurrence on the ear, scalp and elsewhere has been noted. The median age of presentation is about 55 years and the sex ratio is approximately equal. Patients are predominantly white. Lesions are usually asymptomatic, but tenderness, numbness, burning or anesthesia may result from perineural invasion which is frequent.
In one large review [Am J Clin Oncol 2010; 33: 125-127], lymph node involvement occurred in only 1% of patients, and only 1 case in 223 was metastatic. Although MAC causes high morbidity because of its locally aggressive nature, overall survival is similar to the normal population.
Surgical excision with careful attention to margins (e.g. Mohs) is the treatment of choice. Sending the final layer of Mohs for permanent paraffin-embedded sections is recommended. Patients need long term follow up to make sure there is no recurrence. Careful palpation of the scar should be done. A complete skin examination yearly is also appropriate since these patients may be subject to other skin cancers. Although radiation therapy can induce MAC, it has been used as primary treatment, and may be considered for lesions on the face where surgery would give a poor cosmetic outcome.
The 8 mm or so bulge on the upper lip just to the right of the midline turned out to be a large deeply invading MAC.
This article shows how a very large defect may result with surgery as MACs can be extensively locally invasive. From Plast Reconstr Surg Glob Open. 2014 Nov; 2(11): e254.