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Purpose: The effectiveness of current follow-up guidelines after breast cancer treatment is uncertain. Tailored surveillance based on patient age and tumor characteristics may be more adequate. This study aimed to analyze the frequency of ipsilateral locoregional recurrences (LR) and second primary breast cancers (SP) detected outside of scheduled surveillance and to analyze risk factors associated with these events.

Methods: Patients with surgically treated early-stage breast cancer from the Malmö Diet and Cancer Study (MDCS), 1991–2014 (n = 1080), and the Västernorrland region, 2009–2018 (n = 1648), were included. Clinical and pathological information on the primary tumor and recurrences was retrieved from medical records. The mode of recurrence detection was defined as detection within (planned) or outside (symptomatic) of scheduled surveillance.

Results: The median follow-up was 6.5 years. Overall, 461 patients experienced a recurrence. The most common initial event was distant metastasis (47%), followed by locoregional recurrence (LR) (22%) and second primary (SP) (18%). 56% of LR and 28% of SP were identified outside of scheduled surveillance. Logistic regression analysis revealed that younger age (under 50 years) (OR 2.57, 95% CI 1.04–6.88), lymph node-positive breast cancer (OR 2.10, 95% CI 1.03–4.39) and breast cancer of the HER2 positive subtype (OR 5.24, 95% CI 1.40–25.90) were correlated with higher odds of detecting a recurrence outside of planned surveillance.

Conclusion: Most recurrent events were detected outside of scheduled surveillance, particularly for locoregional recurrences. Risk-based surveillance, which takes into account patient and tumor characteristics, might be more suitable for specific patient subsets.