High resolution mapping of consistent leiomyoma breakpoints in chromosomes 12 and 14 to 12q15 and 14q24.1

A substantial percentage of uterine leiomyomas are cytogenetically characterized by consistent, clonal chromosome abnormalities, including t(12;14)(q14-15;q23-24) and other rearrangements of 12q14-15 that occur without any visible 14q changes. The partly similar banding characteristics of these two regions have hitherto precluded exact mapping of the 12q and 14q breakpoints to any particular band, let alone their assignment to subbands. In the series of four myomas presented here, in which one tumor had inv(12q), two t(12;14), and one a three-way t(7;12;14), we were able to achieve high resolution banding (550 band stage) of the rearranged chromosomes in several metaphases. This enabled us to assign a 12q breakpoint to 12q15 in all tumors and, in the three cases informative in this regard, the 14q breakpoint to 14q24.1. The more precise breakpoint mapping considerably narrows down the area that must be examined with molecular genetic methods in order to identify the gene loci that are rearranged in leiomyomas with 12q and 14q aberrations. It will also help determine to what extent leiomyoma rearrangements of 12q involve the same loci that are affected in 12q changes in other tumor types, e.g., in pleomorphic adenomas of the salivary gland, in lipomas, and in myxoid liposarcomas. At present it seems that the breakpoint in 12q may be cytogenetically identical in the three benign tumors, whereas it in myxoid liposarcomas appears to be more proximal.