New classification for advanced breast cancer patients experiencing disease progression during salvage treatment: a single-center retrospective cohort study

BACKGROUND: Attributed to inter-tumor heterogeneity, the therapeutic effect of salvage treatment is diverse and different malignant lesions might manifest various therapeutic responses among advanced breast cancer (ABC) patients. The present study aimed to explore the influence of the mode of lesion response on the subsequent treatment and to subclassify ABC patients for precise prognosis prediction. METHODS: Based on the inclusion and exclusion criteria, ABC patients were retrospectively collected and followed up in the Guangdong Provincial Hospital of Chinese Medicine between 2018 and 2021. The treatment responses of all malignant lesions were evaluated according to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 criteria. Testing subclassified models were constructed based on different assembly mode of progressed malignant lesions for further classification of ABC patients experiencing disease progression following first-line treatment. Multivariate survival analyses were performed to assess the second-line progression-free survival (PFS) of various subgroups and screen the suitable classification model. The most suitable model was utilized to classify enrolled ABC patients as a heterogeneous progression-disease (Heter-PD) group or homogeneous progression-disease (Hom-PD) group. Univariate analysis and multivariate Cox regression survival analyses were performed to assess the prognostic value of each variable. RESULTS: A total of 70 ABC patients experiencing disease progression after first-line treatment were enrolled into the analyses and underwent median follow-up of 10.36 months. We constructed 3 testing models and Model C (Hom-PD was defined when all the target and non-target lesions were evaluated as progression, with or without new lesions) could further distinguish ABC patients with worse survival. The second-line progression-free survival (PFS) times were significantly different between two groups (11.04 vs. 6.07 months, P=0.034). For ABC patients retaining partial medication after disease progression of first-line treatment, the Heter-PD group showed a tendency of better second-line PFS than the Hom-PD group (13.18 vs. 3.61 months, P=0.430). CONCLUSIONS: Based on the disease progression mode after first-line treatment, the classification model could classify ABC patients as Hom-PD and Heter-PD subgroups, which manifest distinct prognoses during the sequential treatment. For Heter-PD patients, retainment of partial medication might be a rational choice for second-line therapy.