Are breast cancer and bone cancer related?

Sort of: Breast cancer can spread to the bones; this is called metastasis. This is the closest relationship.

Metastatic Disease: What makes any cancer "evil" is its ability to break away from its organ of origin and travel thru the body taking up residence in other organs; this secondary organ involvement is referred to as metastases. The bones are a common site of breast ca mets. Rx hinges upon chemotherapy to kill as many cancer cells as possible, supplemented by radiation therapy to control its growth (and symptoms).