I think there may be an issue with the training data here as I cannot reproduce this output with random input:
net = BreastCancerModel().cuda()
x = torch.randn((8, 3, 50, 50), device='cuda')
print(net(x))

tensor([[0.0419],
            [0.0497],
            [0.0391],
            [0.0421],
            [0.0439],
            [0.0445],
            [0.0450],
            [0.0524]], device='cuda:0', grad_fn=<AddmmBackward>) 

Can you print an example of the input to the model (e.g., the first batch)?