Genetic Characterization of Myoid Hamartoma of the Breast

Abstract

Background/aim: Myoid hamartoma of the breast is a very rare benign lesion of which only a few cases have been reported. The pathogenesis is unknown and nothing is known about its genetic constitution. We report here the genetic characterization of a myoid hamartoma of the breast.

Materials and methods: Cytogenetic, fluorescence in situ hybridization (FISH), RNA sequencing, reverse transcription polymerase chain reaction (RT-PCR), and Sanger sequencing analyses were performed on a myoid hamartoma of the breast.

Results: G-Banding analysis of short-term cultured tumor cells yielded the karyotype 46,XX,t(5;12)(p13;q14)[6]/46,XX[4]. FISH showed rearrangement of the high mobility group AT-hook 2 (HMGA2) gene. RNA sequencing detected fusion of HMGA2 (12q14) with a sequence from 5p13. RT-PCR together with Sanger sequencing verified the HMGA2-fusion transcript.

Conclusion: Myoid hamartoma of the breast may be pathogenetically related to benign connective tissue tumors with HMGA2 rearrangements, such as pulmonary hamartomas, lipomas, myolipomas, and leiomyomas.

Keywords: HMGA2 rearrangement; Myoid hamartoma of the breast; RNA sequencing; Sanger sequencing; chromosome translocation; cytogenetics; fluorescence in situ hybridization; reverse transcription polymerase chain reaction.

Figure 1. Microscopic examination of the myoid hamartoma of the breast. A: Hematoxylin and eosin (HE)-stained section showing the area of glandular tissue next to area of smooth muscle differentiation (upper right), ×40. B: HE-stained section showing smooth muscle tissue and glandular tissue, ×100. C: H&E-stained section showing smooth muscle tissue and some fat cells, ×100. D: Immunohistochemical examination showing expression of desmin in the smooth muscle component.

Figure 2. Genetic examination of myoid hamartoma of the breast. A: Partial karyotype showing the der(5)t(5;12)(p13;q14), der(12)t(5;12)(p13;q14), and normal chromosomes 5 and 12. Breakpoint positions are indicated by arrows. B: Fuorescence in situ hybridization on a metaphase spread with the high mobility group AT-hook 2 (HMGA2) break-apart probe. A normal yellow signal is seen on chromosome 12, a red signal on der(12) (arrow), and a green signal on der(5) (arrow). C: HMGA2-fusion sequence obtained from the raw data after RNA sequencing using the deFuse software package. The G|G junction of HMGA2 with sequence from chromosome band 5p13 is highlighted with red. The position of the forward HMGA2-929F1 and reverse 5p13R primers are highlighted with green. D: Partial sequence chromatogram of the cDNA amplified fragment showing the junction position of HMGA2 and sequence from chromosome band 5p13 (arrow). The stop codon TAA is underlined. E: The putative protein which contains amino acid residues 1-83 of HMGA2 (accession number NP_003474.1) as well as nine amino acid residues VHSTGEKQS from the 5p13 sequence (highlighted with yellow).