Primary cutaneous histiocytoid or signet-ring cell carcinoma represents an extremely rare adnexal neoplasm that most frequently presents on the eyelid but more rarely may present in the axilla. As this tumor can resemble metastatic carcinoma with signet-ring cells, especially lobular carcinoma of the breast, it can often present a diagnostic challenge. We present a case of cutaneous signet-ring cell carcinoma presenting in the axilla and outline the challenges of diagnosing this rare malignancy.

Aplasia cutis congenita (ACC), congenital absence of skin, is most common on the scalp but may rarely occur on the trunk and limbs. It is a physical finding that can occur in isolation or as part of a heterogeneous group of syndromes. It can affect localized to widespread areas of absent or atrophic, scarred skin at birth. We report a case of ACC of the distal right forearm associated with radial dysplasia in a newborn boy. According to the Frieden classification of ACC, this case, along with other similar reported cases, highlights the need to adjust the classification scheme commonly used for ACC so that it reflects the associated limb abnormalities with ACC of the extremities. Only five cases describing the association of radial dysplasia with ACC of the arm were found in the literature. Greater awareness of this association may allow for early intervention and better outcomes in children with ACC of the extremities.

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