neoplasmid

Neoplasmid is a term that appears in some cancer biology discussions to describe plasmid-like, extrachromosomal DNA elements found in tumor cells. It is not a universally adopted or formally standardized term in the scientific literature, and its precise definition can vary by source. In many contexts, elements that would be referred to as neoplasmids are better described by widely used terms such as extrachromosomal DNA (ecDNA) or double minutes.

In concept, a neoplasmid would be a small, circular or otherwise circularizable DNA molecule located outside the main chromosomal set, distinct from bacterial plasmids but sharing the feature of autonomous replication. These elements can carry amplified oncogenes or other regulatory sequences that contribute to abnormal gene expression. Their presence can be associated with intratumoral heterogeneity and rapid evolutionary dynamics within a cancer cell population.

Origins and structure of neoplasmids are linked to genomic rearrangements and amplification mechanisms observed in cancers, such as breakage-fusion-bridge cycles and selective pressure for growth advantages. Depending on the tumor type, ecDNA-like elements may vary in size and gene content, and they can be lost or gained across clonal lineages, affecting treatment responses.

Detection typically relies on cytogenetic and sequencing approaches, including fluorescence in situ hybridization (FISH), whole-genome or circle sequencing, and specific ecDNA enrichment methods. Clinically, the concept highlights the role of extrachromosomal genetic elements in oncogene amplification and tumor evolution, though neoplasmid is not yet a standardized label in diagnostic practice.

See also: Extrachromosomal DNA in cancer, ecDNA, double minutes, oncogene amplification, tumor heterogeneity.