Abstract P6-04-08: Microarray Characterization of 24 Cases of Pure Mucinous Carcinoma of the Breast

Abstract

Abstract Background: Mucinous carcinoma of the breast has been shown to be a distinct histological entity with a better clinical prognosis than invasive ductal carcinoma, NOS. Only a few cases have thus far been studied by molecular analysis. The purpose of this is study is to further evaluate the genomic changes in mucinous carcinoma of the breast. Design: 24 pure mucinous breast carcinomas with available fresh frozen tissue were retrieved from our files. The cases were reviewed for histologic grade (SBR), mitoses, percent mucin, intracytoplasmic mucin, type A or B mucinous carcinoma, and estrogen receptor (ER) and progesterone receptor (PR) expression. Follow-up was available for 13 patients and included 4 recurrences. Representative sections of the tumors were dissected from the normal tissue present in the blocks and were assayed by Agilent (Santa Clara, CA, USA) human genome CGH microarray kit 105A. Analysis was performed using Agilent (Santa Clara, CA, USA) genomic workbench 5.0 software. Results: The 24 mucinous carcinomas were composed of 19 type A and 5 type B mucinous carcinomas, including 21 with >60% mucin and 3 with <60% mucin. Seven cases contained intracytoplasmic mucin. Tumors were grade 1 in 20 cases and grade 2 in 4 cases. Mitotic count per 10hpfs was 0 or 1-2 in 19 cases and >3 in 5 cases. ER was positive in all cases, and PR was positive in all but 4 cases. Analysis of the genome arrays showed that 17 of the cases had a complex level of genetic instability with three or more (up to 15) of the chromosomes showing instability while four show only one or two chromosomes affected. On the other hand, there are no abnormalities found in four of the cases. The most frequently affected chromosome is chromosome 1 which is involved in 12 of the cases, with three cases showing 1p partial loss/full loss, and nine cases showing 1q partial gain/full gain. Gains were also commonly seen in 8p, 8q, 11q, 16p, 17q and 20q. Losses were most frequently seen in 6q, 11q, 16q and 17p. Four of five Type B tumors exhibited a complex pattern, and all four grade 2 tumors had a complex pattern. Of the tumors that recurred, three of four had a complex pattern of genetic instability. Conclusions: Evaluation of pure mucinous carcinomas studied showed a high level of genomic complexity with multiple chromosomal changes in most cases. Tumors that were grade 2 and mucinous type B tumors tended to be of higher complexity than grade 1 and type A mucinous tumors. The most commonly affected chromosomes include chromosomes 1, 6, 8, 11, 16, and 17. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-04-08.