Acantholytic squamous cell carcinoma is usually associated with hair follicles, not acantholytic actinic keratosis, and is not "high risk": Diagnosis, management, and clinical outcomes in a series of 115 cases.

BACKGROUND: Acantholytic squamous cell carcinoma (aSCC) is regarded as a high-risk variant of cutaneous squamous cell carcinoma (SCC). Acantholytic actinic keratosis (aAK) has been regarded as a precursor risk factor for aSCC. However, supporting evidence is limited. OBJECTIVE: We sought to document clinical features, histologic features, management, and outcomes in a series of aSCC cases. METHODS: Definitions of aSCC, aAK, and aSCC arising in association with aAK were applied to a consecutive series of aSCC cases. Clinical characteristics and outcomes were obtained from electronic medical records. RESULTS: Of 115 aSCC cases (103 patients, mean age 71.8 years), actinic keratosis was present in 23% (27/115) but only 7.8% (9/115) exhibited associated aAK. Ten cases (10/115, 9%) fulfilled strict histologic criteria for follicular SCC as previously defined, but 50 of 115 (43%) of our aSCC cases exhibited predominant involvement of follicular epithelium rather than epidermis. Clinical outcome (median follow-up, 36 months) was available in 106 of 115 (92%). One patient experienced regional extension (parotid), and 1 patient experienced a local recurrence (nose). No disease-related metastases or deaths were documented. LIMITATIONS: This was a single-institution retrospective study from the United States. CONCLUSIONS: The presence of acantholysis in cutaneous SCC does not specifically confer aggressive behavior, a finding that may inform clinical practice guidelines.

Crater/ulcerated form of infundibular squamous cell carcinoma: A possible distinct entity as a malignant (or high-grade) counterpart to keratoacanthoma.

Follicular squamous cell carcinoma (SCC) with infundibular differentiation includes the common and crater forms of infundibular SCC. We previously considered the crater/ulcerated infundibular SCC to be a progressive condition of the common form and histopathologically studied an additional five cases of the crater/ulcerated infundibular SCC, the results of which suggested the following characteristic histopathological features and possible developmental process in this type of SCC: (i) a considerable number of continuous hyperplastic follicular infundibula, which may develop at the beginning of the disease; (ii) hyperplastic infundibula exhibiting an abrupt or gradual transition to the SCC component, which frequently change relative to the neoplastic infundibular canal; and (iii) the presence of multiple sites of branching of the neoplastic infundibular canals and/or complete involvement of large cysts in the neoplastic process over the center of the lesion, resulting in ulceration. Based on these histopathological findings, we considered that crater/ulcerated infundibular SCC involve a considerable number of continuous follicular infundibula from the start, although some cases may develop from the common form. We also emphasize the possible aggressive biological behavior of the crater/ulcerated form. Keratoacanthoma (KA) is a unique, benign or borderline malignant neoplasm exhibiting follicular (infundibular/isthmic) differentiation characterized by the involvement of continuous follicular infundibula in multiples. From this standpoint, we consider that crater/ulcerated infundibular SCC is possibly related to KA in terms of histogenesis and is a malignant (or high-grade) counterpart of KA.