Cemento-ossifying fibromas are considered odontogenic neoplasms and only occur in the tooth-bearing areas of the jaws according to the current WHO classification. Differential diagnosis of extragnathic lesions include this benign lesion and will be discussed during the course.

History: 47y old male patient undergoing curretage of the right paranasal sinus due to chronic sinusitis. Incidental finding. Benign fibro-osseous lesion, in keeping with ossifying fibroma of non-odontogenic type.

Based on the morphology and ALK positivity a diagnosis of inflammatory myofibroblastic tumor was made.

Diagnosis: This is a tubulocystic carcinoma high-grade or poorly-differentiated foci (sarcomatoid) foci, and these tumors are associated with fumarate hydratase deficiency. This patient died of metastatic carcinoma.

A radical nephrectomy and lymphadenectomy were performed. Most of the tumor resembled a tubulocystic carcinoma but there were foci of a higher grade glandular and sarcomatoid component.

Discussion 2: Central necrosis and calcifications are common, mimicking high grade DCIS. Loss of E-Cadherin expression confirms the lobular phenotype. p120 shows cytoplasmic staining.

Discussion 1: Pleomorphic LCIS is a variant of LCIS, characterized by large dyscohesive cells with marked nuclear pleomorphism, >4 times the size of a lymphocyte, equivalent to the cells of high-grade DCIS.

Diagnosis: Lobular carcinoma in situ (LCIS), pleomorphic type