Whats the classification of breast cancer metastasis?

Staging: Breast cancer staging is described as t (tumor size), n (lymph node metastases) and m (metastases to sites like bone, lung, etc). In a simplified short answer: stage 0 is non-invasive breast cancer, stage 1 is no spread to lymph nodes, stage 2 and stage 3 has lymph node spread and larger tumors, and stage 4 would have metastases to other organs.