medwireNews: Women with interval breast cancers (IBCs) diagnosed within 1 year of a negative mammogram screening result have poorer disease-specific survival than those with screen-detected cancers, US study findings indicate.
Zhenzhen Zhang (OHSU Knight Cancer Institute, Portland) and co-investigators say the poor prognosis “might not be due to delayed diagnosis but rather to distinct biological characteristics associated with the cancer.”
They add: “For instance, increased lymph node involvement is often seen in IBCs and cannot be accounted for entirely by delayed diagnosis but rather may be due to a unique biology.”
The study included 3019 postmenopausal women who were diagnosed with breast cancer at a median 68.5 years of age while participating in the Women’s Health Initiative study.
Of these, 1969 (65.2%) were diagnosed through protocol-mandated screening while 1050 (34.8%) were IBCs, including 30.9% diagnosed within 1 year of a mammogram with negative results and 69.1% diagnosed between 1.0 and 2.5 years of a negative result.
The researchers report in JAMA Network Open that, compared with screen-detected cancers, IBCs diagnosed within 1 year of a negative mammogram were significantly larger (mean, 1.97 vs 1.43 cm), were more likely to have lobular histology (13.0 vs 8.1%) and lymph node involvement (27.1 vs 17.0%), and were more frequently at a regional (28.4 vs 17.3%) or distant stage (3.7 vs 0.6%).
Unadjusted analyses showed that the risk for breast cancer-specific mortality was significantly higher for women with an IBC diagnosed within 1 year of a negative mammogram than for those whose cancers were detected by screening, at a hazard ratio (HR) of 1.92.
The significantly increased mortality persisted after adjusting for trial group, molecular subtype, waist-to-hip ratio, histologic characteristics, and either tumor size (hazard ratio=1.46) or lymph node involvement (hazard ratio=1.44) but was no longer significant when both tumor size and lymph node involvement were accounted for.
By contrast, there was no significant difference in prognostic factors or survival between the women with IBCs detected between 1.0 and 2.5 years of a negative mammogram and those whose breast cancers were detected by screening.
Zhang and co-authors conclude that their study “adds to a growing body of literature that argues for the development of novel approaches to detect life-threatening cancers currently missed by mammographic screening.”
They suggest: “Women who present with breast cancer symptoms at the time of negative screening mammogram results should either be recalled more frequently, have a shorter screening period, or undergo another imaging modality, such as ultrasonography or magnetic resonance imaging.”
In addition, “the combination of germline genomic testing with mammography may help distinguish indolent breast cancers from aggressive breast cancers detected by screening,” the team remarks.
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JAMA Netw Open 2020; 3: e207227