Invasive Cuniculatum Carcinoma of the Groin Mimicking Hidradenitis Suppurativa

To the Editor: INTRODUCTION According to World Health Organization classification of skin tumors, carcinoma cuniculatum (CC) is a rare, well-differentiated cutaneous squamous cell carcinoma. It was originally described on the soles by Aird et al1 and rarely arises in other locations. CC has a characteristically undulant architecture and exhibits locally aggressive behavior. Clinically, it appears as an outward-growing, wart-like painful tumor that might ulcerate and produce an unpleasant discharge.2 Histopathological diagnosis requires a deep biopsy, and the pathological examination is difficult due to rare cellular atypia and mitotic figures. It is mainly based on the abundance of crypts and branching sinuses, which inspired the name “cuniculatum”.1 We report a case of CC in a rare location on the right groin with regional inguinal lymph nodes, muscular, and bone invasions. The initial clinical presentation was reminiscent of hidradenitis suppurativa. CLINICAL CASE A 65-year-old man with a history of hypertension and heart failure, without any history of inflammatory skin dermatosis, was hospitalized for a large suppurative lesion of the right groin on April 2022, progressing since more than 4 years. Clinically, the patient had compromised general status, and locally presented a large purplish deeply infiltrated plaque of the right groin and the adjacent thigh with numerous purulent sinuses and crypts, as well as exophytic budding and vegetating skin lesions (Figs. 1A, B). A diagnosis of hidradenitis suppurativa was initially evoked. Deep skin biopsy was performed, and the histopathological examination showed an exophytic and endophytic squamous tumor proliferation consisting in a hyperplastic, acanthotic, papillomatous epidermis, which invaginates deeply in the skin with marked orthokeratotic and parakeratotic hyperkeratosis, and minimal cytological atypia, that led to the diagnosis of CC (Figs. 2A–C). Moreover, on clinical examination, a regional inguinal lymph node of the right groin was found. Whole-body CT and Emission positons tomography scan (Fig. 3) confirmed a massive regional lymph node involvement and contiguous bone and muscular invasion. The case of this patient was discussed at our multidisciplinary oncology meeting. No curative treatment could be proposed. Surgical treatment was ruled out because the disease was too advanced locally, and chemotherapy was contraindicated due to severe heart failure. Unfortunately, the patient died on July 2022 due to the worsening of his skin malignancy and deterioration of his general condition.FIGURE 1.: A, Multiple purulent sinuses of the right groin; B, Profound crypt of the right posterior thigh.FIGURE 2.: A, B, Endophytic proliferation with invagination into the dermis (hematoxylin and eosin, original magnification ×80); C, Discrete cytonuclear atypia in the lesion (hematoxylin and eosin, original magnification ×600).FIGURE 3.: Emission positons tomography-computed tomography showing invasion of bone, lymph nodes, and deep skin.DISCUSSION To the best of our knowledge, this is the first case of CC in this localization without any underlying ulcerative or inflammatory dermatosis. Although various etiological factors have been incriminated including repeated microtrauma, radiodermatitis, chronic wound, Human Papilloma Virus infection, or hidradenitis suppurativa; in our case, there was no preexisting dermatosis.2,3 Atypical localizations and unusual clinical presentations of CC have already been described in the literature, notably on the buttocks in a recent case of a 49-year-old woman treated medically and surgically for hidradenitis suppurativa for 13 years.3 In this case, CC appeared to be a long-term complication of hidradenitis suppurativa, unlike to our case. Besides, McArdle et al cited 4 cases of CC localized on sacrogluteal region without any underlying inflammatory dermatosis. Another Japanese case report described a verrucous carcinoma at the border between the scrotum and inner aspect of the thigh in a 53-year-old man,4 which differs from our case by the absence of purulent sinuses and deep crypts. CC rarely metastasizes to lymph nodes and visceral organs,5 but it can progressively invade deeper tissues, such as muscles and bones. In general, it has a favorable prognosis, with a 5-year survival rate of 75%.2 CONCLUSION We present a special case of CC due to its atypical clinical presentation, unusual localization, and, most unusually, severe local progression leading to the patient's death.