Plantar Verrucous Carcinoma Misdiagnosed as a Recalcitrant Wart: Diagnostic Pitfalls and Destructive Local Progression

Chronic plantar verrucous lesions represent a frequent diagnostic challenge, as they often mimic benign conditions such as plantar warts. However, the continued assumption of a benign diagnosis despite lack of therapeutic response reflects not only delayed biopsy, but also insufficient consideration of relevant differential diagnoses, including cutaneous malignancies and deep infections. Among these, verrucous carcinoma, particularly its plantar variant, carcinoma cuniculatum, is a rare but locally aggressive subtype of cutaneous squamous cell carcinoma characterized by slow growth, low metastatic potential, and progressive local destruction. We report the case of a 76-year-old male with an 8-year history of a verrucous lesion on the right foot, demonstrating progressive enlargement and initially managed as an infectious and inflammatory condition with multiple topical and systemic therapies, without clinical improvement. Over time, the lesion evolved into a large exophytic mass with ulceration, malodorous discharge, and significant functional limitation. Imaging studies revealed suspicious inguinal lymphadenopathy without confirmed distant metastasis. A deep incisional biopsy established the diagnosis of well-differentiated squamous cell carcinoma, verrucous variant (carcinoma cuniculatum). Due to extensive locoregional involvement and a high risk of functional morbidity, the tumor was deemed initially unresectable. Systemic treatment with pembrolizumab (200 mg every three weeks) was initiated in the setting of locally advanced unresectable disease. After six cycles, the patient demonstrated a partial clinical and radiological response, with sustained disease control and good tolerance after eleven cycles, allowing reassessment for potential surgical management. This case illustrates how prolonged diagnostic delay, in this instance, nearly eight years, can lead to locally advanced disease, limiting initial surgical options. It underscores the importance of early biopsy and comprehensive diagnostic reassessment in chronic verrucous lesions, as well as the potential role of immunotherapy as a therapeutic alternative in selected patients with advanced verrucous carcinoma.