Magic mushroom: all is not as it seems.

Background The late adverse effects of radiotherapy are caused by microvascular injury or depletion of differentiated cells. Methods Here we describe a clinical case of a late and unusual complication related to radiotherapy, in a patient with a history of squamous cell carcinoma of the anal canal. Results The patient presented with a large perianal vegetating lesion suspicious of local recurrence, however the biopsy of the lesion did not show malignancy. Conclusion Fortunately, all is not as it seems, and what appeared as a suspected relapse turned out to be a benign reactive lesion, consequence of radiotherapy.