In this paper, we propose a generative AI-based data augmentation framework that integrates synthetic image sharing into ultrasound images for breast cancer diagnosis to address the limited data availability and non-independent, identically distributed (NID) data issues that limit the effectiveness of federated learning (FL). We train two class-specific Deep Convolutional Generative Adversarial Networks (DCGANs) to generate synthetic images, and simulate the federated learning environments based on FedAvg and FedProx algorithms using three public datasets: BUSI, BUS-BRA, and UDIAT. The experimental results show that by adding an appropriate number of synthetic images, the average AUC of FedAvg improves from 0.9206 to 0.9237, and that of FedProx improves from 0.9429 to 0.9538, while excessive use of synthetic data leads to performance degradation. This demonstrates that generative AI-based data augmentation can improve the FL results on breast ultrasound image classification tasks.