Hi I'm looking for a free breast cancer x-ray images database

Training a model to save the world huh? Better be labeled correctly. I'm sure no one thought of this before.

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You have the Digital Database for Screening Mammography (DDSM). It's a relatively old database with pre-digital images. But it should be a good start.

http://www.eng.usf.edu/cvprg/mammography/database.html

Good luck!

When looking to expand your dataset, aim for diversity - not just in terms of race, but also in terms of the hospitals and x-ray/diagnostic equipment used.

Examples of models failing when a dataset collected from one hospital is applied to another are well known.