2958 - Impact of Timing of Diagnosis and Breastfeeding on Postpartum Breast Cancer Outcomes

03:00pm - 04:00pm PT

Hall F

Screen: 3

POSTER

Presenter(s)

Dasha Klebaner, MD, MPH - Stanford University Cancer Center, Palo Alto, CA

D. Klebaner¹, N. J. Park¹, K. Stone², S. Crowe³, C. M. Marquez¹, and K. C. Horst¹; ¹Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, ²Department of Surgery, Stanford University School of Medicine, Stanford, CA, ³Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, CA

Purpose/Objective(s):

Pregnancy-associated and postpartum breast cancers (PABC/PPBC) have a worse prognosis than other breast cancers. We hypothesized that patients diagnosed within 2 years postpartum (2-year PP) and those breastfeeding (BF) at diagnosis would have inferior outcomes compared to patients diagnosed 2 to 5 years postpartum (2-5 year PP) or non-BF patients.

Materials/Methods:

Using ICD-9 and ICD-10 codes, we identified PPBC patients diagnosed at our institution 2-year PP or 2-5 year PP following a live birth. Clinicopathologic details, BF status at diagnosis, mastitis in the 6 months preceding diagnosis, and whether presenting symptoms of PPBC were initially attributed to BF or lactational change by either the patient or a provider were ascertained via chart review. Characteristics were compared between groups using chi-square or Kruskall-Wallis tests. Kaplan-Meier analysis was used to assess overall survival (OS) and metastasis-free survival (MFS).

Results:

Between 2002-2024, 60 2-year PP patients and 101 2-5 year PP patients were identified. The 2-5 year PP group was older (median age 39.6 vs 37.4 years, p<.001) and less likely to be BF (7% vs 60%, p<.001) at diagnosis. Patients in the 2-5 year PP group were diagnosed at a lower clinical T-stage (50% vs 20% T1, 36 vs 17% T3-4, p<.001) and N-stage (61% vs 37% N0, 11% vs 29% N2-3, p=.01) compared to the 2-year PP group. There was a trend toward decreased metastasis (3% vs 12%, p=.06) and lower grade (13% vs 5% Grade 1, 55% vs 65% Grade 3, p=.21) at diagnosis for 2-5 year PP vs 2-year PP patients. Estrogen/progesterone receptor positivity and triple-negative disease did not differ between groups, but HER2+ disease was more common among 2-year PP patients (36% vs 17%, p=.012).

Among 2-year PP patients, BF at diagnosis showed a trend toward increased clinical nodal involvement (71% vs 50%, p=.17), metastasis at diagnosis (17% vs 4%, p=.29), and HER2 positivity (44% vs 22%, p=.13). BF patients were significantly more likely to be diagnosed with mastitis in the 6 months preceding PPBC diagnosis (31% vs 4%, p=.03) and to have their PPBC symptoms initially attributed to BF or lactational change (58% vs 4%, p<.001). There was no difference in months postpartum at diagnosis between BF and non-BF patients (median 11.8 months vs 13.5 months, p=.7).

Median follow-up was 54 months. The 2-year PP group had inferior OS (5-year OS 79% [95% CI 67-93] vs 97% [95% CI 93-100], p<.001) and MFS (5-year MFS 74% [95% CI 60-90] vs 93% [95% CI 87-99], p=.003) compared to 2-5 year PP patients. Among 2-year PP patients, there was a trend toward worse OS (5-year OS 74% [95% CI 59-93] vs 86% [95% CI 70-100], p=.08) and significantly worse MFS (5-year MFS 62% [95% CI 45-86] vs 91% [95% CI 75-100], p=.032) for those BF vs not BF at diagnosis.

Conclusion:

Breast cancer diagnosed in the first two years postpartum has a worse prognosis compared to later PPBC. Breastfeeding at diagnosis is associated with inferior outcomes and may lead to delayed diagnosis due to misattribution of symptoms to lactational change.