Sclerosing basaloid proliferation on the nasolabial fold with an unvisualized deep margin
A 67-year-old woman has an 8-mm firm, ill-defined plaque on the left nasolabial fold that has slowly enlarged over 3 years. A 3-mm punch biopsy shows narrow strands and small nests of cytologically bland basaloid cells embedded in dense sclerotic collagen, with several small keratin-filled cysts and a tadpole configuration; the deep margin is not visualized. No retraction clefts or mucin are seen. Immunohistochemistry shows positivity for BerEP4 and p63, patchy EMA in ductal structures, and rare CK20-positive cells. The pathologist reports sclerosing basaloid proliferation, favor desmoplastic trichoepithelioma, but microcystic adnexal carcinoma cannot be excluded. The patient is anxious about a cancer diagnosis and asks whether a simple re-excision is enough.
1. Which features favor microcystic adnexal carcinoma over desmoplastic trichoepithelioma and morpheaform basal cell carcinoma, and how much weight should a single CK20 result carry?
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Features favoring microcystic adnexal carcinoma:
- Deep infiltration beyond the superficial dermis, often into fat, muscle, or perineural spaces, with a tadpole or comma shape in sclerotic stroma.
- Ductal differentiation highlighted by EMA and CEA, with luminal cuticles.
- Perineural invasion, the single most decisive feature, though it is not always present in a small biopsy.
- Cytologically bland cells, which is a trap: microcystic adnexal carcinoma is deceptively bland.
Features favoring desmoplastic trichoepithelioma: a small, superficial, well-circumscribed lesion with horn cysts, calcification, no perineural invasion, and scattered CK20-positive Merkel cells.
Features favoring morpheaform basal cell carcinoma: retraction clefts, mucin, and a BerEP4-positive, EMA-negative phenotype; basal cell carcinoma lacks true ducts.
Weight of CK20: a few CK20-positive cells support desmoplastic trichoepithelioma, but a single patchy result is weak evidence, sampling can miss Merkel cells, and rare CK20 cells have been reported in other adnexal tumors. It should never override architecture and depth.
2. What does the unvisualized deep margin mean, and how should the lesion be sampled next?
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A biopsy that does not visualize the deep margin cannot exclude microcystic adnexal carcinoma, which is defined in part by deep infiltration and perineural spread. The reported favor desmoplastic trichoepithelioma is a provisional interpretation on a partial sample, and the clinical setting (nasolabial fold, indurated, slowly enlarging plaque) is classic for microcystic adnexal carcinoma.
The next step is a deep incisional or excisional biopsy that includes subcutaneous fat, oriented for margin assessment, with sampling of any perineural structures. If the lesion is on the face and the diagnosis remains uncertain, referral to a dermatologic surgeon or Mohs surgeon for diagnostic excision with margin control is appropriate. Imaging with MRI is indicated if perineural invasion is found or if the lesion is large or symptomatic.
A second superficial punch would simply reproduce the same diagnostic problem and delay definitive management.
3. What treatment would you recommend once the diagnosis is settled, and why is simple re-excision potentially inadequate?
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Simple re-excision is potentially inadequate because microcystic adnexal carcinoma is locally aggressive with extensive subclinical spread and a high recurrence rate. It tracks along nerves and can extend well beyond visible or palpable margins. The standard of care is Mohs micrographic surgery or wide local excision with complete margin assessment, often with multidisciplinary involvement if perineural invasion is extensive. Radiation may be considered for unresectable or recurrent disease.
Before committing the patient to a morbid facial operation, the diagnosis must be settled. I would explain that the current report is provisional and that a definitive diagnosis requires a deeper specimen. If the final diagnosis is desmoplastic trichoepithelioma, conservative excision is adequate; if it is morpheaform basal cell carcinoma, Mohs is also appropriate. The patient's anxiety is best addressed with a clear staged plan rather than a rushed excision.