BACKGROUND AND OBJECTIVES: Breast cancer in young patients (<= 40 years) (YBC) is an uncommon disease and is the leading cause of cancer death in women in their age. The objective of this study was to characterize and identify potential differences in the molecular and clinical features of breast carcinomas from patients <=40 years versus a cohort of older premenopausal counterparts as a control matched by breast cancer subtype. METHODS: We performed a retrospective analysis of a prospectively maintained database that included 427 premenopausal patients diagnosed with an invasive breast carcinoma from 2005 to 2013 at University of Tsukuba Hospital. We selected 286 patients separated in two groups, the study group with young women <=40 years old and with no or unknown BRCA mutation, and a second group with women over 40 years. Data related to clinical and pathological features from both groups such as tumor size, nodal status, histological grade, Ki 67 labeling index, estrogen and progesterone receptor, HER2 overexpression, and pregnancy related information were obtained from medical records and we used the statistic model of chi-squared to compare the two groups. Survival analysis was performed using the Kaplan Meier method. RESULTS: The median age of the 93 patients ≤ 40 year was 34.6 years, and 193 patients >40 years were included in the control group (median age 46.4 years). There were 22 pregnancy associated breast cancer (PABC) cases in YBC cohort. Ductal carcinoma was the most common histological subtype in both groups. By subtype, 65% of YBC presented an immunohistochemical luminal subtype, compared to 41% in PABC and 77% in older patients (p=0.01). Triple negative and HER2 profiles were 19% and 16% in YBC versus 36% and 23% in PABC and 12% and 11% in control respectively (p=0.01). The YBC cohort had a larger tumor (24% of YBC had size tumor > 5 cm, versus 9% in control, p=0.01), and more frequent nodal involvement (48% in YBC vs 39% in control, p<0.05), the higher proportion of Ki67 >30% (35% in YBC vs 24% in control, p<0.05). Limiting to YBC, subtype nor PABC were not identified as an independent risk factor for disease free survival, but luminal subtype in YBC demonstrated worse survival compared with those in control. CONCLUSIONS: We observed more aggressive tumor characteristics in patients diagnosed with breast cancer at <=40 years, or PABC patients compared to older premenopausal patients. Clinical implications of age on tumor behavior were different according to subtypes. Further research to overcome worse survival for luminal YBC is warranted.

Citation Format: Hiroko Bando, Mai Furuya, Aya Sawa, Akiko Iguchi, Tatsuhiko Ikeda, Shotaro Shima, Hisato Hara. Characterization of of the tumor and risk factors in Japanese young breast cancer patients [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-10-16.