Purpose: Safely postponing the use of chemotherapy is important for quality of life maintenance in patients with hormone receptor-positive advanced breast cancer. In previous studies, a combination of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) and fulvestrant prolonged the time to chemotherapy (TTC). In this study, we used real-world data to evaluate TTC in the context of CDK4/6i therapy. Methods: We performed a retrospective chart review of women with estrogen receptorpositive, human epidermal growth factor receptor 2-negative advanced breast cancer treated at the Aichi Cancer Center Hospital. The patients were categorized into having received CDK4/6i therapy first (n = 41), second (n = 33), and none at all (n = 67). The change in TTC among the groups was examined. Results: The median follow-up time was 13.8, 27.5, and 30.3 months in the CDK4/6i (first), CDK4/6i (second), and non-CDK4/6i groups, respectively. The median progression-free survival (PFS) with first-line therapy for metastasis was 30.0, 11.9, and 13.0 months, respectively (CDK4/6i [first] vs. non-CDK4/6i; p = 0.018, CDK4/6i [second] vs. non-CDK4/6i;p = 0.383). The median TTC was not reached in the CDK4/6i (first) group, was 39.1 months in the CDK4/6i (second) group, and was 44.2 months in the non-CDK4/6i group (CDK4/6i [first] vs. non-CDK4/6i; p = 0.880; CDK4/6i [second] vs. non-CDK4/6i; p = 0.407). The nonCDK4/6i group with TTC ≥ 60 months included more cases of secondary endocrine therapy resistance (p = 0.017), no perioperative chemotherapy (p = 0.021), and a longer disease-free interval (p = 0.093). Conclusion Although PFS was significantly longer in the CDK4/6i (first) group than in the non-CDK4/6i group, TTC did not significantly differ among the three groups in real-world data. The non-CDK4/6i group showed a long TTC in patients with late recurrence and low risk at the primary lesion site, who benefited greatly from hormone monotherapy.

Purpose: Fine-needle aspiration cytology (FNAC) of axillary lymph nodes (AxLNs) is performed to diagnose nodal metastasis in patients with breast cancer. Although the sensitivity of ultrasound-guided FNAC for identifying AxLN metastasis is in the range of 36%–99%, whether sentinel lymph node biopsy (SLNB) should be performed for neoadjuvant chemotherapy (NAC) patients with negative FNAC results is uncertain. This study aimed to determine the role of FNAC before NAC in the evaluation and management of AxLN in early breast cancer patients. Methods: We retrospectively analyzed 3,810 clinically node-negative (a lymph node with no clinical metastasis without FNAC or radiological suspicion of metastasis with negative FNAC results) patients with breast cancer who underwent SLNB between 2008 and 2019. We compared the positivity rate of sentinel lymph nodes (SLNs) between patients who received and those who did not receive NAC with negative FNAC results or without FNAC and axillary recurrence rate in the neoadjuvant group with negative SLNB results. Results: In the non-neoadjuvant (primary surgery) group, the positivity rate of SLNs in patients with negative FNAC results was higher than that in patients without FNAC (33.2% vs. 12.9%; p < 0.001). However, the SLN positivity rate of patients with negative FNAC results (false-negative rate for FNAC) in the neoadjuvant group was lower than that in the primary surgery group (3.0% vs. 33.2%; p < 0.001). After a median follow-up of 3 years, one axillary nodal recurrence was observed, which was a case from the neoadjuvant non-FNAC group. None of the patients in the neoadjuvant group with negative FNAC results had axillary recurrence. Conclusion The false-negative rate for FNAC in the primary surgery group was high;however, SLNB was the proper axillary staging procedure for NAC patients who have clinically suspicious AxLN metastases on radiologic examination but negative FNAC results.