Monosomy 13 in Mammary Myofibroblastoma

Abstract

Background/Aim: Myofibroblastoma of the breast is a rare benign mesenchymal tumor whose morphology is similar to that of spindle-cell lipoma. The few hitherto genetically investigated mammary myofibroblastomas have been shown to have had loss of material from chromosome 13, changes that are also common in spindle-cell lipoma. Our aim was to add to the existing knowledge of genetic aberrations in mammary myofibroblastoma by investigating another such tumor. Materials and Methods: Cytogenetic and array comparative genome hybridization (aCGH) analyses were performed on a surgically removed mammary myofibroblastoma from a 76-year-old man. Results: Shortterm cultured cells from the tumor showed the karyotype 45, XY,idem,add(19)(q13)[cp2]. aCGH detected loss of one entire chromosome These findings add to the evidence that loss of 13q material is typical of mammary myofibroblastomas.Mammary myofibroblastoma is a rare benign mesenchymal tumor of the breast reported for the first time in 1987 in 11 male and 5 female adult patients as a lesion "largely composed of myofibroblasts arranged in fascicular clusters with interspersed bands of hyalinized collagen" (1). Until 2018, fewer than 90 tumors had been reported (2). In most of the publications (3-12), single cases were described adding to the evidence that these are rare tumors. Genetic information on mammary myofibroblastoma is available for 21 tumors: two were examined by G-banding and karyotyping (10); ten by fluorescence in situ hybridization (FISH) analysis using a probe specific for the forkhead box O1 (FOXO1) gene which maps to chromosome sub-band 13q14.11 (11,(13)(14)(15); eight using a FISH probe for the RB transcriptional corepressor 1 (RB1 located on 13q14.2) gene (16, 17); and one tumor was examined by OncoScan as part of a copy-number variant study of 11 benign mesenchymal tumors (18). Because of the rarity of the tumor and the limited genetic information, we present here another mammary myofibroblastoma examined by banding cytogenetics and array comparative genome hybridization (aCGH). Materials and MethodsEthics statement. The study was approved by the Regional Ethics Committee (Regional komité for medisinsk forskningsetikk Sør-Øst, Norge; http://helseforskning.etikkom.no; 2010/1389/REK sør-øst A). Written informed consent was obtained from the patient. The Ethics Committee's approval included a review of the consent procedure. All patient information has been de-identified. Case Report. A tumor was removed from the breast of a 76-year-old male patient. It measured 5×4×3 cm, had a solid consistency and was well demarcated from the surrounding adipose tissue (Figure 1A). Microscopically, the tumor was partly well demarcated from surrounding adipose tissue in some areas (Figure 1B) but in other areas less so (Figure 1C). The tumor cells were elongated and intermingled with hyaline fibers (Figure 1D). Loosely arranged spindle cells with indistinct cell borders were seen (Figure 1E). Mitotic figures were sparse. Necrosis was not present. No ductal structures w...