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FDCTGAN: Client-local CTGAN-augmented federated learning for imbalanced breast cancer classification

Salehpour A, Balafar MA, Souri A

Technology and health care : official journal of the European Society for Engineering and Medicine, 2026

Abstract

ObjectiveFederated learning enables collaborative medical model development without centralizing patient records; however, client-level class imbalance may reduce sensitivity to malignant cases. This study evaluated FDCTGAN, a client-local CTGAN-augmented federated learning framework for imbalanced breast cancer classification.MethodsIn FDCTGAN, each eligible client trained a local conditional generative adversarial network and generated synthetic malignant records equal to 50% of its local class deficit. Raw and synthetic data remained on the originating client. Only feature extrema were shared once per outer fold, while classifier parameters were exchanged through Federated Averaging. Five-fold stratified cross-validation on the Wisconsin Diagnostic Breast Cancer dataset compared FDCTGAN with Vanilla FL, Local SMOTE-FL, Centralized CTGAN-FL, and Centralized Pooled learning. Each augmentation method was evaluated using three augmentation seeds and three classifier seeds, producing nine stochastic runs per fold.ResultsUnder full-batch local training, FDCTGAN increased malignant-class recall from 0.9448 ± 0.0206 with Vanilla FL to 0.9632 ± 0.0117. However, the paired recall difference was not statistically significant using a two-sided Wilcoxon signed-rank test (p = 0.125; five folds), and an increase in false positives accompanied the improvement. With a batch size of 32, FDCTGAN no longer outperformed Vanilla FL in malignant recall. Local SMOTE-FL provided the strongest…

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