Inflammatory myofibroblastic tumours (IMT) are spindle cell neoplasms most commonly seen in the lungs, with a wide variety of less common extrapulmonary sites including the mesentery, omentum, and intrabdominal sites. On cytological evaluation, these tumours can be difficult to diagnose, given the morphological mimics of other submucosal spindle cell neoplasms, which may be compounded by the relatively small amount of tissue and the uncommon nature of the diagnosis. Immunohistochemical staining and molecular studies for the ALK gene can prove useful for diagnosing this tumour. We present the cytological features of an IMT occurring in the rectum, the differential diagnoses, useful immunohistochemical staining patterns, and the additional finding of a novel ALK-fusion in this entity.

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Atypical fibrous histiocytomas are an uncommon but benign variant of dermatofibroma where the neoplastic cells can feature cytological atypia constituted by prominent nuclear enlargement, pleomorphism and multinucleated giant cells. Though these can have a degree of atypia, they have a benign course and a failure to recognize these tumors as benign can lead to misdiagnosis and overtreatment, particularly in patients with Li-Fraumeni syndrome who are known to be predisposed to various malignancies. Here, we report a patient with atypical fibrous histiocytomas and multiple pleomorphic fibroma-type lesions in the setting of Li-Fraumeni syndrome.

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