Allelic loss in squamous cell carcinomas of the larynx: discordance between primary and metastatic tumors.

The mutational inactivation of suppressor genes, a process required for cancer progression, generates new genetic subclones within a tumor. The allelic losses that frequently unmask these mutations serve not only as markers of the chromosomal locations of these genes but also as clonal fingerprints of the shifting relationships between these genetically heterogeneous cell populations. The rise of the metastasis-competent subclone to dominance within the primary tumor should be reflected in the similarity of the genetic fingerprints of the primary tumor and its resultant metastases. We have tested this hypothesis by comparing the patterns of allelic loss of individual primary laryngeal squamous cell carcinomas and their resultant cervical lymph node metastases at 16 different genetically polymorphic loci on 15 chromosome arms. Although primary tumors and metastases both frequently lose heterozygosity on the same chromosome arms (3p, 9p, 9q, 13q, and 17p), five of the 12 metastases differed from their primary tumors at one or two of the loci examined. Discordance between the two tumor cell populations from the same patient is suggestive of either subclone heterogeneity within the primary tumor at the time of establishment of the metastasis or further clonal evolution of both tumors after metastasis.