BACKGROUND AND PURPOSE:

• Interval breast cancers (IBCs) are defined as cancers that develop after a negative mammogram but before the patient’s next screening
  • IBCs appear to have a worse prognosis
• Irvin et al. (JAMA Network Open, 2020) sought to compare the prognostic features and mortality rate of associated with IBCs vs  breast cancers detected by screening

METHODS:

• Cohort study
• Data source
  • Women’s Health Initiative (WHI) study
  • The Women’s Health Initiative study recruited participants from 1993 to 1998 and followed up for a median of 19 years | The present study includes data collected through March 31, 2018
• Population included in this study
  • Age 50 to 79 years
  • Compliant with breast cancer screening
  • Developed breast cancer
• Study design
  • Collected data: Mammography data | Tumor characteristics | Demographic data
  • Breast cancers detected by screening and IBCs were defined based on
    • Mammogram history
    • Date of last mammogram
    • Type of visit
    • Results of examination
  • Interval breast cancers were subdivided into those occurring
    • Within 1 year following negative mammogram
    • Between 1 and 2.5 years following negative mammogram
• Primary outcome
  • Breast cancer–specific mortality for
    • Breast cancer detected by screening
    • IBCs
• Secondary outcomes
  • Prognostic and tumor characteristics for each group

RESULTS:

• 3019 women were compliant with screening developed breast cancer
  • Mean (SD) age at enrollment: 63.1 (6.8) years
  • Mean (SD) age at diagnosis: 68.5 (7.1) years
• Breast cancer diagnoses
  • Interval breast cancers: 1050 cases
    • 30.9% were diagnosed between 1 and 2.5 years after negative mammogram
  • Breast cancer detected by screening: 1969 cases
• Comparing IBCs within 1 year vs screening detection group
  • More lobular histologic characteristics
    • IBCs: 13.0%
    • Screening detected cancers: 8.1%
  • Larger tumor size
    • IBCs: 1.97 cm
    • Screening detected cancers: 1.43 cm
  • Higher clinical stage
    • Regional
      • IBCs: 28.4%
      • Screening detected cancers: 17.3%
    • Distant
      • IBCs: 3.7%
      • Screening detected cancers: 0.6%
  • More lymph node involvement
    • IBCs: 27.1%
    • Screening detected cancers: 17.0%
• IBCs diagnosed within 1 year were associated with increased breast cancer–specific mortality when compared to cancers identified by screening
  • Unadjusted hazard ratio (HR) 1.92 (95% CI, 1.39 to 2.65)
• Breast cancer–specific mortality risk was increased for IBCs diagnosed within 1 year after adjusting for trial group, molecular subtype, waist to hip ratio and histologic characteristics and either
  • Tumor size: HR 1.46 (95% CI, 1.03 to 2.08) or
  • Lymph node involvement: HR 1.44 (95% CI, 1.03 to 2.01)
• However, when adjusted for both tumor size and lymph node involvement, results, breast cancer-specific mortality association was no longer statistically significant
  • HR 1.34 (95% CI, 0.96 to 1.88)
• IBCs diagnosed between 1 and 2.5 years from a mammogram were not different from breast cancers detected by screening for prognostic factors or mortality

CONCLUSION:

• Interval breast cancers within 1 year of negative mammogram overall were associated with worse survival compared to breast cancers detected at time of scheduled screening
• However, the authors state

The poor prognosis for women with IBCs diagnosed within 1 year after negative mammogram results might not be due to delayed diagnosis but rather to distinct biological characteristics associated with the cancer

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.

Learn More – Primary Sources:

Comparison of Mortality Among Participants of Women’s Health Initiative Trials With Screening-Detected Breast Cancers vs Interval Breast Cancers

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