Squamous cell carcinoma uncommonly presents as a primary neoplasm of the nail. When occurring in the periungual region, this malignancy may mimic a wide variety of infectious, inflammatory, and neoplastic disorders, including the common wart. We present the case of 62-year-old man with subungual squamous cell carcinoma in situ that for many years was treated as a verruca.
Key words. Carcinoma, squamous cell; pathology; surgery; nail diseases, microbiology; papillomavirus; classification. (J Fam Pract 1994; 39:384-387)
The pathogenesis of subungual squamous cell carcinoma in some cases may involve chronic infection, radiation, trauma, arsenic exposure, or the human papillomavirus (HPV). The treatment of this condition historically has relied upon local surgical extirpation, including partial amputation of the affected digit; however, other modalities, including the Mohs micrographic technique, may be equally effective and provide superior functional results in some cases.
A 62-year-old man was evaluated for a recalcitrant lesion involving the subungual and periungual areas of his left middle finger. The lesion had been present for 32 years and had been treated on numerous occasions as a subungual wart. Various methods had been used, including: topical keratolytic agents, electrodesiccation, cryosurgery, and blunt dissection. Despite these therapeutic efforts, the lesion slowly progressed.
The patient's medical history was notable for coronary artery disease and nephrolithiasis. He had a 40-year history of cigarette smoking. A physical examination revealed a skin-colored, hyperkeratotic verrucous nodule involving the nail bed of the left middle finger (Figure). Mild swelling, erythema, scaling, and verrucous changes of the periungual region were present as well. Most of the nail had been destroyed. There was no lymphadenopathy, and the remainder of the physical examination was unremarkable.
An incisional biopsy revealed squamous cell carcinoma in situ (Bowen's disease). Radiograph and magnetic resonance imaging studies demonstrated no evidence of bony involvement.
The lesion was excised by partial amputation of the distal phalanx. The amputated specimen again revealed squamous cell carcinoma in situ. The patient has had no recurrences during 3 years of follow-up.
Subungual squamous cell carcinoma is an uncommon entity reported by Schreiber to account for only 2 cases of a series of 14,415 cases of skin cancer. Tomsick and Menn reported a somewhat higher incidence, having accumulated 8 cases from a series of 3000 cases of skin cancer. Goldminz and Bennett found only 171 cases in the world literature.
The etiology of subungual squamous cell carcinoma is unclear. Pathogenic factors proposed for some cases have included chronic paronychia, trauma, roentgenography, ultraviolet radiation, arsenic, and dyskeratosis congenita. Human papillomavirus (HPV) has been implicated in the pathogenesis of some cases that did not have other known predispositions. In a study of 10 cases of subungual squamous cell carcinoma using a dot-blot hybridization technique, Moy and co-workers found DNA sequences homologous to HPV in 8 of 10 lesions. Six of these were identified specifically as HPV type 16. Similar results were reported by Ashinoff et al, who identified HPV type 16 DNA in 5 of 7 squamous cell carcinomas of the finger and nail bed through the polymerase chain reaction.
HPV type 16 has been closely associated with cervical carcinoma, and with some cases of condylomata acuminata and bowenoid papulosis.[7-10] The demonstration of this virus with known oncogenic potential in such a significant proportion of subungual squamous cell carcinomas suggests that in some cases these lesions may develop in subungual warts that eventually undergo malignant transformation.
Subungual squamous cell carcinoma has been reported in patients ranging from 19 to 94 years of age, but it occurs most commonly in the 6th and 7th decades of life. The thumb is the most common location, and the digits of the hands are involved much more frequently than those of the feet.
Clinical manifestations vary and may mimic onychomycosis, chronic paronychia, chronic osteomyelitis, eczema, glomus tumor, subungual exostosis, verruca vulgaris, pyogenic granuloma, fibroma, keratoacanthoma, melanoma, or metastases.[4,11,12] With involvement of the nail matrix, the nail may become dystrophic and onycholysis may occur. Secondary infections are common. Bleeding, ulceration, or a nodular surface suggests the possibility of an invasive lesion.
The clinical course tends to be characterized by indolent local growth.[2,4,12,13] The duration of signs and symptoms from onset to the time of diagnosis has ranged from several months[2,13,14] to as long as 32 years (present case). Although invasion of underlying bone has been found in about 18% of cases, it is generally regarded as a low-grade malignancy. Fatal metastases have been reported in only 2 patients.[15,16] This is in contrast to squamous cell carcinoma occurring elsewhere on the hand, in which invasion of tendon or bone is accompanied by regional lymph node metastases in 30% of cases.
The diagnosis of subungual squamous cell carcinoma is established by biopsy. In addition to the typical histopathologic features of squamous cell carcinoma, findings suggestive of verruca vulgaris are commonly present. This further supports the role that HPV may play in the pathogenesis of these neoplasms.
There is controversy in the literature pertaining to the association of Bowen's disease with a predisposition to develop other malignancies of both cutaneous and systemic origin. Graham and Helwig reported the occurrence of internal malignancies in 24 of 35 (68.6%) patients with Bowen's disease. In addition to the patients with internal cancers, four from this series developed metastasizing cutaneous malignancies. Subsequent studies, including another by Graham and Helwig, found the association of Bowen's disease with internal cancers to be less dramatic, although still significant with a reported incidence of systemic cancers ranging from 13.4 to 29.1%.[20-22]
Some have stated that the association between Bowen's disease and internal malignancies is most significant in patients in whom Bowen's disease occurs on non-sun-exposed sites, that is, on cutaneous regions generally protected by clothing. Other investigations,24-26 including a large study from Denmark, found no statistically significant increase in the incidence of internal malignancies in patients with Bowen's disease. Two reviews of the literature[27,28] concluded that the available data do not support the existence of a predisposition to the development of internal cancers in patients with Bowen's disease.
Seven patients have been reported to have subungual Bowen's disease involving two or more digits.[4,29-31] Two of these patients had been exposed to significant amounts of ionizing radiation.[4,31] Three cases of subungual Bowen's disease have been reported in association with uterine cervical carcinoma.[6,17,31] We are unaware of any other reports of malignancies occurring in association with Bowen's disease of the nail.
Because the number of reported cases of subungual Bowen's disease is very small, it is impossible to conclude whether the presence of this condition should be considered a marker for a tendency to develop additional cancers. It is likely that patients who have had significant exposure to ionizing radiation have an increased risk of developing subsequent cutaneous lesions. Because of the close association with HPV type 16, it is prudent to examine the genitalia when evaluating patients with subungual squamous cell carcinoma, including those with Bowen's disease. Certainly female patients should be monitored closely for the development of cervical carcinoma.[6,32]
The treatment of choice for subungual squamous cell carcinoma is surgical ablation. Either partial or total amputation of the affected digit has been the treatment used most frequently in the recent past. In light of the rather indolent biology of squamous cell carcinoma of the nail unit, many authors strongly advocate Mohs micrographic surgery, a frozen tissue technique that affords cure rates as high as 96% for this malignancy and achieves optimum preservation of normal tissue.[3,4,11] This is particularly important for lesions occurring on the thumb, where even partial amputation results in a significant loss of hand function. Alternatively, simple surgical excision, cryosurgery, electrosurgery, or radiation therapy may be appropriate in some cases. Amputation is still the preferred therapeutic modality for those with osseous involvement.[3,11,12] Regional lymph node dissection is warranted only in cases with palpable lymphadenopathy.[13,34,35]
We opted to treat our patient's neoplasm by means of partial amputation of the distal phalanx after considering the extent of the lesion, its location on the third digit of the patient's nondominant hand, and the patient's wishes. He has been quite pleased with the functional and cosmetic results.
Some have suggested that biopsies should be obtained before initiating treatment of chronic periungual lesions. We concur with this proposal in cases such as ours, in which the morphology of the nail and periungual region is significantly disrupted. However, longstanding cases of nail or periungual conditions that have classic historical and clinical features of benign nail diseases, such as chronic paronychia, onychomycosis, or periungual verrucae, may warrant a therapeutic trial before histopathologic examination. A biopsy should be considered in cases that fail to respond to a reasonable trial of conventional treatment.
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