Loss of Heterozygosity on Chromosome 1 and 9 and Hormone Receptor Analysis of Metastatic Malignant Melanoma Presenting in Breast

Abstract

Malignant melanoma (MM), the most common metastatic solid tumor to involve the breast, may present as a diagnostic problem, frequently requiring the use of ancillary studies for accurate diagnosis. The implication of hormonal interplay is strong since metastatic MM to the breast is seen nearly always in women. However, the role of hormonal status as a predisposing factor in the development of this entity is largely unresolved. A number of chromosomal loci, including ip36 and 9p2l-22, appear to harbor critical genes important to melanoma tumorigenesis, and additionally chromosome 9q22.3-31. We wanted to know if metastatic MM in breast showed chromosome lp and 9p genetic alterations (loss of heterozygosity) similar to those that occur in primary cutaneous MM, and whether additional 9q LOH changes are present. Hormonal receptor status of the metastatic MM was also determined. We identified 20 patients with known MM metastatic to the breast, which we analyzed with the following genetic markers: D9S12 (9q22.3), D9S171 (9p21), IFNA (9p22), and DlS450 (ip). Visually directed microdissection was performed on archival histologic slides containing both tumor and adjacent normal breast epithelium, followed by single-step DNA extraction and polymerase chain reaction (PCR) amplification for evaluation of loss of heterozygosity (LOH) for the above-listed markers. Immunohistochemical (IHC) stains for estrogen receptor (ER) and progesterone receptor (PR) was performed on 10 of the cases. Twelve of the 20 cases contained DNA suitable for PCR amplification following direct visualization microdissection. Four of 8 (50%) informative cases showed LOH at 9p21 with D9S171. Ten cases were heterozygous for IFNA, with 2 cases (20%) showing LOH at this locus. These particular cases also showed LOH at 9p21. One of 9 (11%) informative cases showed LOH for DlS450 (Ip36). Five cases were heterozygous for D9S12, and 2 1-22 (50%) and lp36 (11%), as previously described in primary cutaneous MM. Additional LOH was observed at the 9q22.3-31 locus (40%). We suggest this locus to be investigated for harboring potential genes important in the tumorigenesis of cutaneous MM.