[129] Molecular Phenotype of Pregnancy Associated Breast Cancers (PABC) in a Large Cohort of Young Women

S Demski, S Gelber, J Marotti, K Cole, S Kereakoglow, K Ruddy, E Brachtel, L Schapira, S Come, V Borges, P Schedin, E Warner, E Winer, A Partridge, L Collins. Beth Israel Deaconess Medical Center, Boston; Dana Farber Cancer Institute, Boston; Dartmouth-Hitchcock Medical Center, Lebanon; Massachusetts General Hospital, Boston; University of Colorado Cancer Center, Denver; Sunnybrook Odette Cancer Centre, Toronto, Canada

Background: The increase in breast cancer risk during pregnancy and post-partum is well known; however the molecular phenotype of PABCs has not been well studied. A genomic signature specific to the pregnant breast, which remains present postmenopausally, has been identified. Given this, we investigated whether the time interval since pregnancy affects the phenotype of breast cancers in parous vs. nulliparous young women.
Design: We examined molecular phenotype, determined by histologic grade on central review and biomarker status by report, in relation to time since pregnancy in a prospective study (n=359) of young women (≤40yrs) with breast cancer. Parity was ascertained from study questionnaires. Using tumor grade and biomarker expression, cancers were categorized as luminal A or B, HER2-type and triple negative (TN).
Results: Overall, 67% of cancers were ER+ and 29% were HER2+. There were no differences in the distribution of molecular phenotype according to time interval since pregnancy.

Distribution of molecular phenotype by interval between last pregnancy and diagnosis

Molecular Phenotype	Nulliparous N=132 (37%)	<= 2 years N=54 (15%)	>2-5 years N=74 (21%)	>5 years N=99 (28%)	Total patients N=359
Luminal A (ER/PR+, HER2-, grade 1 or 2)	54 (41)	17 (31)	18 (24)	34 (34)	123 (34)
Luminal B (ER/PR+, HER2+ or ER/PR+, HER2-, grade 3)	45 (34)	19 (35)	26 (35)	34 (34)	124 (35)
HER2 type (ER-, PR-, HER2+)	9 (7)	6 (11)	13 (18)	9 (9)	37 (10)
Triple negative (ER, PR, HER2-)	24 (18)	12 (22)	17 (23)	22 (22)	75 (21)

However, nulliparous young women were more likely to develop luminal A cancers compared to parous women (41% vs. 30%; unadjusted chi square p=0.04) and appeared less likely to develop HER2-type and TN cancers (7% vs. 12%, p=0.10; 18% vs. 22%, p=0.34).
Conclusions: The distribution of breast cancer molecular phenotype is similar among parous young women irrespective of time interval since parturition. Nulliparous young women appear more likely to develop luminal A cancers. Whether the difference in molecular phenotypes of PABCs vs. cancers in nulliparous women is due to genomic alterations in the parous breast remains unknown. Effects of a prior pregnancy appear consistent across a 5-year period.
Category: Breast

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 37, Monday Morning