Testicular embryonal carcinoma: a morphologic study of 180 cases highlighting unusual and unemphasized aspects.

A total of 180 consecutive testicular cancers containing a component of embryonal carcinoma (EC) were reviewed to assess the morphologic features of the EC component. EC mostly (84%) occurred as a component of a mixed germ cell tumor, but 16% were pure. Solid (55%), glandular (17%), and papillary (11%) were the most common primary patterns (predominant architectural pattern occupying at least 50%), whereas other less common primary patterns included nested (3%), micropapillary (2%), anastomosing glandular (1%), sieve-like glandular (<1%), pseudopapillary (<1%), and blastocyst-like (<1%). Occasionally, EC developed predominantly in the context of polyembryoma-like (6%) and diffuse embryoma-like ("necklace" pattern) (3%) proliferations. In all, 69% had secondary architectural patterns, the most frequent being glandular (31%), papillary (14%), and solid (12%). An appliqué appearance, in which smudged and degenerate-appearing EC cells appear "applied" to the tumor periphery, was common (67%). EC cells with clear cytoplasm and distinct cell membranes (seminoma-like) were present in 11%, and dense lymphocytic infiltration and granulomatous inflammation were seen in 7% and 3%, respectively. Features simulating yolk sac tumor and teratoma were also seen: pseudoendodermal sinuses (34%), columnar cells (20%), and secretory-type subnuclear cytoplasmic vacuoles (6%). Syncytiotrophoblast cells were frequent (46%). Intratubular EC, typically partly necrotic and calcified, occurred in 24%. The associated stroma was more often non-neoplastic (53%) than neoplastic (29%). The rarity of some poorly characterized patterns of EC (micropapillary, blastocyst-like, anastomosing glandular, and sieve-like glandular) and some that overlap with those of other germ cell tumors, as well as some uncommon cytologic features, may result in misinterpretation, potentially impacting management. The association with other more common patterns and typical cytologic features, together with simple awareness of these variant morphologies, are helpful in establishing an accurate diagnosis of EC.