Caught in the Act: Intercalated Duct Lesion Associated with Adenoid Cystic Carcinoma Harboring a MYBL1::NFIB Fusion.

Intercalated duct lesions (IDLs) are putative precursors notably associated with epithelial myoepithelial carcinoma and basal cell adenoma. We report the novel transition of IDL to adenoid cystic carcinoma (AdCC) in the parotid gland of a 38-year-old male. The patient presented with a longstanding mass and subsequently underwent parotidectomy. Microscopically, the 3.9 cm tumor consisted mainly of tubular/cribriform AdCC. However, the periphery showed three IDL foci with a similar immunophenotype. Next generation sequencing demonstrated a MYBL1::NFIB fusion. We thus further expand the spectrum of tumors that can transition from IDL.