It is very difficult to find reliable figures about the incidence or prevalence of squamous cell carcinoma in HS patients since there are very few publications describing follow-up of HS patients. Mostly isolated didactic cases are described, which increase clinical vigilance but do not provide predictive data. The risk of squa-mous cell carcinoma in HS has been estimated at between 1.7% and 3.2% . Case reports however also allow the reader to form a clinical picture of a given problem when they are sufficiently numerous. In fact, there may be as many as 100 [87, 92] cases of squamous cell carcinoma arising from HS reported so far in the literature: these include cases arising from so-called acne conglobata of the buttocks/perineum or postsacral skin [5, 52-54, 70-93] and cases of malignant degeneration occurring in patients with "long-standing pilonidal disease, with a mean duration of 23 years" . Both these diagnostic groups may potentially be confused with HS.
Reviewing the published cases there seems to be a clear predominance in men, since only eight cases of squamous cell carcinoma have been de-
The clinical picture is rather stereotypical. Lesions occur almost exclusively in the perineal area, but one case of axillary cancer in HS has been reported . In almost all cases, squa-mous cell carcinoma arises in an individual with a long-lasting HS, usually between 10 and 30 years of duration, but extremes of 3 years [78, 92] and 50 years  have been reported. Lesions start insidiously with usual sinus tracts and oozing, but the recent onset of increased pain and discharge, as well as the presence of firm infiltrated subcutaneous nodules and/or extensive and ulcerated granulation tissue should alert the physician, especially if the disease has lasted for many years and keeps worsening. The tumour may rapidly enlarge and is usually resistant to any treatment including surgery except for wide excision. The diagnosis of squamous cell carcinoma is sometimes a surprise during excision for HS and discovery of an indurated area  or a histological surprise [88, 92], requiring a wide re-excision.
Patients may present with metastatic lymph nodes. Three cases with associated paraneoplas-tic hypercalcaemia have been published [75, 77, 83] and, in one of these, the presenting symp toms could be attributed to a paraneoplastic parathyroid-hormone-like protein . Other paraneoplastic symptoms may occur and one case has been published describing a paraneo-plastic neuropathy in association with HS-re-lated squamous cell carcinoma .
Clinically, the following diagnosis may be considered: anal fistula, lymphogranuloma venereum, granuloma inguinale, Crohn's disease, tuberculosis cutis, Nocardia infection, actino-mycosis, tularaemia, chronic pyoderma gan-grenosum and erysipelas.
Biopsy should be performed to exclude malignancy. In fact, diagnosis relies on biopsy, which should be repeated in cases of suspicion, even if the first biopsy samples are reassuring, because the histological differential diagnosis with pseudoepitheliomatous hyperplasia may be very difficult [88, 91]. The clinical picture should always guide the physician; for instance, a very fast and extensive recurrence after surgery indicates a high suspicion of malignant disease.
The only curative treatment is wide excision with re-excision if margins are too close. Surgeons insist on the necessity of assessment of margins because the tumour often spreads more widely than its external appearance would suggest . Wounds heal surprisingly well in the perineal area. It has been suggested that early reconstruction may hide a recurrence, and secondary healing by granulation without colosto-my has therefore been advocated .
Squamous cell carcinoma is a relatively che-moresistant tumour [76, 77, 85]. Radiotherapy is usually ineffective because of the extent and volume of tissue to be irradiated [72, 76, 85]. So both treatments should be considered only as palliative treatments.
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