Thymic Tumor With Adenoid Cystic Carcinoma-Like Features: A Study of a Clinically Favorable Case Followed for 9 Years.

Thymic tumors with adenoid cystic carcinoma-like features are true rarities, with only 6 cases reported. Our knowledge of their clinical behavior is insufficient. We present a case of a noninvasive cribriform tumor that was followed, including a 4-year period after tumor resection and radiation therapy, for a total of 9 years. The tumor was purely epithelial. It was positive for keratins (AE-1/AE-3, CK19, 34βE12,CK5/6), MOC-31, P63, P40, CD10, and MYB, and was negative for myoepithelial or neuroendocrine markers. Presence of cell processes, desmosome-like junctions with tonofilaments and multifocally reduplicated basal lamina was noted on ultrastructural examination. Two signals of the MYB gene per cell were detected by fluorescence in situ hybridization. No monosomy or translocations of the gene were found. Although additional clinical studies are necessary, it seems that indolent behavior of cribriform noninvasive subset of these tumors may be anticipated.