Abstract PS1-06-26: Fewer cancers in post-treatment surveillance among patients initially staged using contrast-imaging

Abstract Purpose: Women with a past history of breast cancer (PHBC) are at risk of local recurrence or new breast malignancy and guidelines recommend routine surveillance imaging. We previously reported our experience of contrast-enhanced mammography (CEM) for local staging of screen-detected cancer and for surveillance of women with a PHBC [1,2]. In the current study we evaluate whether including CBI at diagnosis is associated with different surveillance outcomes, including recall rates and cancer detection rates (CDR). Methods: A retrospective cohort study included women with early breast cancer or DCIS managed at a tertiary breast service in Australia who underwent surveillance involving contrast imaging. To maintain consistency in exposure to contrast-based surveillance, our analysis was restricted to patients who underwent their first surveillance CEM within 3 years of diagnosis. Outcomes were reported from the first round of CEM surveillance up to the first subsequent cancer diagnosis or 5 years from the index diagnosis, whichever occurred earlier. Outcomes were compared according to CBI use (either CEM or Magnetic Resonance Imaging (MRI)) at initial diagnosis. Outcome measures included overall CDR, surveillance tumour characteristics (stage, size, grade, laterality), recall rates, false positive rates, PPV1 (recalls leading to a cancer diagnosis) and PPV3 (biopsies leading to a cancer diagnosis). Statistical tests included two-sample tests of proportions and logistic regression. Results: The analysis included 1,107 women diagnosed between December 2014 and June 2022, comprising 594 who underwent CBI at diagnosis (355 CEM, 202 MRI, 37 both) and 513 without. The CBI group was slightly younger on average (mean 64.1 vs 66.6 years, p=0.0001), and more recently diagnosed (proportion diagnosed 2019-2022 75.6% vs 38.2%). Across the cohort, 3,879 surveillance episodes were evaluated, with patients undergoing an average of 3.6 rounds in the CBI group and 3.4 rounds in the non-CBI group (p=0.0497). During surveillance, 53 women were diagnosed with cancer, with a significantly lower proportion in the CBI group (3.5% vs 6.2%, p=0.0357) and this difference remained significant after adjusting for age and date at index diagnosis (OR 0.51 (95% CI 0.27-0.93, p=0.028)). Of these, 32 were invasive cancers and 21 were DCIS (one pleomorphic LCIS). Patients without CBI at diagnosis demonstrated a higher rate of surveillance-detected contralateral malignancy (2.5% vs 0.8%, p=0.0264). Surveillance-detected cancers did not differ by tumour behaviour (invasive vs DCIS, p=0.4), grade (p=0.2) or invasive size (p=0.8). Interval cancer rates were low (0.8/1000 episodes) and did not differ between groups. Recall rates after surveillance imaging were comparable between groups (5.3% in the CBI group vs 6.2% in the non-CBI group, p=0.234), as were false positive recall rates (4.2% vs 4.4%, p = 0.805), PPV1 (18.8% vs 29.4%, p=0.0648) and PPV3 (30.9% vs 40.0%, p=0.249). Conclusion: Women with early breast cancer who underwent CBI at diagnosis had significantly fewer cancers detected during early surveillance. This suggests that using more sensitive local staging at diagnosis may allow earlier identification and treatment of synchronous disease that would otherwise manifest as early ipsilateral or contralateral events. Accordingly, this will reduce the burden of breast cancer for patients, with expected improvements in longer-term outcomes. References 1) MacCallum C, Elder K, Nickson C, et al. Contrast-Enhanced Mammography in Local Staging of Screen-Detected Breast Cancer. Ann Surg Oncol. 2024 Oct;31(10):6820-6830. 2) Matheson J, Elder K, Nickson C, et al. Contrast-enhanced mammography for surveillance in women with a personal history of breast cancer. Breast Cancer Res Treat. 2024 Nov;208(2):293-305. Citation Format: T. W. Yang, A. Rose, J. Matheson, K. Elder, C. MacCallum, C. Nickson, G. B. Mann. Fewer cancers in post-treatment surveillance among patients initially staged using contrast-imaging [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-06-26.