Impact of the COVID-19 pandemic on breast cancer diagnosis and treatment trends in Japan.

Background: There is no comprehensive report regarding which patient groups were disrupted by the COVID-19 pandemic in Japan having universal health insurance system. To provide the guidance regarding how to act in future pandemics, we investigated the changes in breast cancer (BC) diagnosis and treatment during the COVID-19 pandemic.

Methods: The trends of monthly data were calculated in relation to the variables of a total of 291,018 primary BCs registered on the Japanese National Clinical Database between January 2018 and April 2021.

Results: An analysis of the nationwide data during the pandemic showed 9% decrease of newly identified BC compared with before the pandemic. The impact was more relevant in the 40-50, 51-60 and 61-70-years age groups (13%, 8% and 9% decrease, respectively). The most substantial reduction was noted in patients identified through screenings without symptoms with a 17% decrease. These effects were also apparent in cT1, cN0, cStage 0, and cStage I (11%, 9%, 8% and 11% decrease, respectively). In breast surgery procedures, there was a notable decrease in breast-conserving surgery (13%) as well as post-operative radiation therapy (11%). During this period, strategies using neoadjuvant endocrine therapy or chemotherapy were implemented to avoid treatment delays for especially Stage I patients (1.5 folds increase).

Conclusions: We have identified the patient groups that are more vulnerable to the effects of the pandemic. The changes during the pandemic might provide the guidance regarding how to act in future emergencies to minimize disadvantages for BC patients.