Perianal Paget's disease: A rare disorder masking an underlying anorectal carcinoma

Perianal Paget's disease (PPD) is a rare type of cancer, with less than 200 cases reported in the literature. PPD generally affects Caucasian people, most often female, with a peak incidence between the ages of 50 and 80.¹

PPD can present as a primary skin disorder or be associated with different synchronous or metachronous cancers, becoming a complex disorder due to the different pathological processes. Primary PPD has relatively favourable prognosis, with both overall and disease-free survival being approximately 60% at five years.²

In the secondary form, however, with synchronous or metachronous carcinoma of the anal region, based on limited reports, the prognosis is poor.³

We present the case report of a 61-year-old man who was referred to a proctology clinic for lesions in the perianal area associated with local discomfort and pruritus. A first biopsy showed extramammary Paget's disease. The patient was started on conservative treatment based on imiquimod cream and local corticosteroid therapy. Three years later, physical examination detected significant growth of the perianal lesions, with a fungating appearance and spread to the anal canal (Fig. 1). The protocol to rule out association with an underlying visceral cancer was applied to exclude rectal carcinoma with spread to the anus. A complete colonoscopy revealed, inside the anal canal and in the surrounding skin, an ulcerated fungating cancer reaching as far as the rectal mucosa, but without invading the rectal ampulla. The report from the new histological examination described an adenocarcinoma with mucinous differentiation and with the same immunohistochemical pattern as the first biopsy. Imaging tests of chest and abdomen for spread of the cancer revealed pathological involvement of the inguinal lymph nodes and iliac chains bilaterally. The first-line treatment of choice consisted of the surgical approach, involving abdominoperineal resection with end colostomy on the left flank. The definitive histological examination of the surgical specimen was positive for a moderately differentiated mucosecretory adenocarcinoma (TNM-pT3, AJCC 8th edition). To control the residual disease, it was decided to apply locoregional adjuvant radiotherapy to the iliac and inguinal lymphadenopathy. Three months after the intervention, a total body CT was performed which showed no evidence of distant visceral disease.

Figure 1.

Hard, painful, fungating tumour in the perianal region on dystrophic skin, approximately 10 cm long, with small superficial erosions.

Extramammary Paget's disease is a clinicopathological entity with a complex diagnostic classification. The location in the perianal region is important from a prognostic point of view, because of the possibility, in up to 50% of cases, of finding an anorectal carcinoma, the most important prognostic factor for which is the depth of invasion. Tumours with a depth of >1 mm are associated with a worse prognosis when they spread outside the skin to the lymph nodes or other surrounding tissues.

PPD initially presents as an erythematous plaque with scaly and eczematous areas, causing local itching and/or burning. It is important to stress that, when local therapy (corticosteroids or antifungals) is not effective after a certain amount of time, PPD should be suspected and a biopsy of the lesion performed. In late stages it can progress towards the formation of a bleeding, fungating mass, as a harbinger of an underlying cancer.

From a therapeutic point of view, there is no unified treatment protocol available at present, so the choice of management in each case will depend on the type (primary vs. secondary) and extent of the lesion, and on clinical experience.

In cases of secondary PPD, therapeutic success will depend on the oncological approach to the associated carcinoma, combining surgery, radiotherapy and/or chemotherapy. Although as yet there have been no randomised clinical trials comparing it to surgery, radiotherapy can be considered in selected cases as an effective treatment modality and a suitable alternative to extensive surgical excision.⁴

In conclusion, the significance of PPD means that it is essential not only to make the differential diagnosis with other skin cancers, but also to ensure early management of a condition which may be the first metastatic manifestation of an underlying visceral carcinoma.