How would you approach a patient with metastatic colon cancer with biopsy-confirmed bone mets who has a significant decrease in CEA on FOLFOX but develops new bone lesions?

I would assume that the bone lesions became more apparent on imaging due to a response from chemo and not because this is true progressive disease. (See Costelloe et al., PMID 20842228) They were likely there at initiation rather than this being a true mixed response. I would trust your tumor marker...

This scenario is not uncommon in patients with prostate cancer. Clinical features might help differentiate true vs pseudo progression in bone metastases. The following features argue in favor of pseudo progression:

• New bone lesions are seen in the first 3 months of starting systemic therapy
• New bon...