Increased risk of metastasis associated with postpartum breast cancer (PPBC) in women 45 years or younger may persist for 10 years after childbirth, a finding that may give reason to extend the 5-year window currently defining PPBC.
Analysis of more than 700 patients showed that risk of metastasis was approximately twofold higher for a decade after childbirth, with risks about 3.5- to fivefold higher in women diagnosed with stage I or II disease, reported lead author, of the Fred Hutchinson Cancer Research Center in Seattle, and her colleagues. Regardless of parity status, patients diagnosed with stage III disease had poor outcomes.
“The high risk for metastasis is independent of poor prognostic indicators, including biological subtype, stage, age, or year of diagnosis,” the investigators wrote in. “Yet, PPBC is an underrecognized subset of breast cancer, and few studies address the associated high risk for metastasis.”
The cohort study involved 701 women 45 years or younger who were diagnosed with breast cancer between 1981 and 2014. Early cases were retrospective, until the study switched to a prospective method in 2004. The investigators analyzed rates of distant metastasis and looked for associations with tumor cell proliferation, lymphovascular invasion, lymph node involvement, and other clinical attributes. Distant metastasis was defined by spread beyond the ipsilateral breast or local draining lymph node, as detected by physical exam, imaging, and/or pathological testing. The investigators also stained available tumor samples for Ki67 positivity, which is used for prognostic purposes, and to distinguish between ER-positive luminal A versus ER-positive luminal B disease.
Compared with nulliparous patients, women under 45 who were diagnosed with PPBC within 5 years of childbirth were 2.13 times as likely to develop metastasis (P = .009). This risk persisted for 5 more years. Women diagnosed within 5-10 years of childbirth showed a similar hazard ratio, of 2.23 (P = .006). After 10 years, the hazard ratio dropped to 1.6, but this value was statistically insignificant (P = .13). Patients identified with stage I or II disease had more dramatic risk profiles, with hazard ratios of 3.5 and 5.2, for diagnoses up to 5 years postpartum, and diagnoses 5-10 years postpartum, respectively. These findings suggest that, for some patients, the 5- to 10-year window may be the riskiest time for metastasis, and, incidentally, one that has historically been excluded from the definition of PPBC.
In addition, patients diagnosed with estrogen receptor–positive breast cancer within 10 years of childbirth had outcomes similar to those of nulliparous women with estrogen receptor–negative breast cancer, and postpartum women with estrogen receptor–negative breast cancer had worse outcomes than did nulliparous women with the same subtype. Furthermore, PPBC was associated with higher rates of lymph node involvement and lymphovascular invasion. Collectively, these findings suggest that PPBC is generally more aggressive than nulliparous breast cancer. In contrast, Ki67 positivity, identifying the luminal B subtype, was associated with worse outcome regardless of parity status, but this finding was statistically insignificant.
“[T]hese data suggest that stages I and II breast cancer in patients with PPBC diagnosed within 10 years of parturition may be underestimated in their risk for metastasis, as parity status is not currently factored into clinical decision-making algorithms, such as the National Comprehensive Cancer Network guidelines,” the investigators concluded. “In sum, we suggest that poor-prognostic PPBC is an increasing problem that merits more dedicated research.”
The study was funded by the National Cancer Institute, the National Institutes of Health, the U.S. Department of Defense, and other organizations. Dr. Goddard reported funding from the NCI and NIH. Dr. Mori reported financial support from the Department of Defense.
SOURCE: Goddard et al. JAMA Netw Open. 2019 Jan 11.