br Introduction Carcinoma cuniculatum was first described by

Introduction Carcinoma cuniculatum was first described by Aird et al in 1954 as epithelioma cuniculatum. The name is derived from the Latin word cuniculus, meaning “rabbit,” because of its rabbit-burrow-like architecture (appearance of the complex branching of keratin-filled crypts). It is regarded as either a low-grade subtype of squamous cell carcinoma or a variant of verrucous carcinoma. It is characterized by a slow-growing, well-differentiated exo- and sometimes endophytic neoplasm that is often locally aggressive but rarely metastatic. Carcinoma cuniculatum most commonly occurs on the soles. However, lesions occurring in other cutaneous sites have also been reported, known as cutaneous verrucous carcinoma. We are the first to report a patient with carcinoma cuniculatum on the nasal tip, showing the typical histological features of carcinoma cuniculatum with the atypical clinical manifestation, with rapid progression, arising from keratoacanthoma. Moreover, we review the clinicopathological and differential diagnoses of this unusual epithelial neoplasm.
Case report A 74-year-old man presented with a reddish nodule on the nasal tip, exhibiting rapid enlargement within 1 month. He had a past history of LY 2109761 under regular medication control for 6 years and benign prostatic hyperplasia. He denied any type of trauma or chronic inflammation in this region. He also reported no substantial personal or family history of skin disease. On physical examination, the patient was found to have a 1.5-cm well-marginated, erythematous rubbery nodule with central ulceration on the nasal tip (Figure 1A). The clinical differential diagnoses included deep bacterial or fungal infection, keratoacanthoma, basal cell carcinoma, and squamous cell carcinoma. First, an incisional biopsy was performed by our dermatologist, who suspected pilar sheath acanthoma. The patient was then referred to our plastic surgeon for further surgical intervention. An excisional biopsy and full-thickness skin graft resurfacing were performed smoothly. Histologic examination revealed hyperkeratosis, parakeratosis, and acanthosis, resulting in pseudoepitheliomatous hyperplasia compatible with a keratoacanthoma (Figure 1B). However, the resection base margin was not free. Owing to the benign skin lesion, the patient refused further excision and agreed to regular follow-ups in our outpatient clinic. The postoperative wound condition was normal. However, rapid local recurrence with a 1.5-cm verrucous mass was found at the original site 1 month later (Figure 2). Although the appearance of the mass was unlike a typical keratoacanthoma, recurrent keratoacanthoma was suspected. Therefore, the patient underwent further excisional biopsy to determine the nature of the mass. Reconstruction surgery was not performed until the pathology report was finalized. Histologic examination revealed a symmetric tumor consisting of a massively hyperplastic and papillomatous-folded epidermis with marked hyperkeratosis and parakeratosis. The epithelial strands contained numerous keratin-filled cysts, formed crypts, and rabbit-burrow-like, keratin-filled sinus formations (Figure 3A). At deeper levels, the tumor was sharply demarcated by an intact basement membrane compressing the underlying collagen tissue. The keratinocytes appeared well differentiated, without any signs of nuclear atypia. Loss of polarity and horn pearls were absent. However, some parts of the tumor indicated slight evidence of atypia, including nascent focal loss of polarity and nuclear atypia of the keratinocytes, even though the basement membrane in these areas remained intact (Figure 3B). All the features were compatible with carcinoma cuniculatum. Thus, wide excision with 5-mm safe margins and full-thickness skin graft resurfacing were performed smoothly 1 week later. The peripheral and base margins were free. The patient recovered uneventfully, and no recurrence of the lesion was reported over a 62-month period of observation (Figure 4).