blastoid

Blastoid is an adjective used in biology and medicine to denote similarity to a blast or blastula, the early embryonic stage. In developmental biology, blastoid descriptions apply to structures or cells that resemble the proliferative, relatively undifferentiated state of early embryos, including embryoid bodies and other stem-cell–derived models that mimic primitive features of the blastocyst.

In pathology, blastoid describes cells with embryonal-like, primitive morphology. Features often include large cell size, a high nuclear-to-cytoplasmic ratio, prominent nucleoli, and frequent mitotic activity. This morphology is a descriptive finding that can occur across various high-grade neoplasms and can influence diagnostic interpretation and treatment planning. The term frequently appears in reference to the blastoid variant of mantle cell lymphoma, a form known for its aggressive appearance compared with classic mantle cell lymphoma. Because blastoid is a descriptive label rather than a specific diagnosis, it is interpreted within the broader histopathological and clinical context and is distinguished from true lymphoblasts or other lineage-specific blast cells during differential diagnosis.

Related terms include blastomere, blastula, embryoid body, and blastulation. The word derives from Latin blastis or Greek blastos, meaning bud or germ, with the suffix -oid meaning likeness. Its use varies by discipline and is periodically refined by updates in classification systems such as the WHO.