TNM staging categorizes each malignancy by the status of the primary tumor (T), nodal involvement (N) and metastatic disease (M). Individual TNM stages can then be grouped into stage 0, I, II, III, or IV.
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On a side note, PET/CT is rarely used to stage bladder cancer. On a PET/CT, the urinary system including bladder normally appears black (metabolic uptake), obscuring everything within it, making it difficult to detect underlying pathology.
PET/CT is used more for staging/restaging lymphoma, breast cancer, etc.