How do you decide when to pursue malignancy workup for patients with cryptogenic stroke?  

There are no exact guidelines for this. I start with a thorough history and physical exam (including a detailed review of systems, potential carcinogen exposures (like work history and smoking, etc.), family history in both younger and older patients). In low-risk younger patients, I may start with ...

Agree with above. I would also pursue malignancy work-up in this scenario as well: currently on anticoagulation (whether for afib or another medical reason) and has an ischemic stroke on top of that.

I would pursue a malignancy workup in most younger patients with a cryptogenic stroke after the initial search for a vessel or cardiac source was unrevealing. I would also consider a malignancy workup in selected older patients with cryptogenic stroke, such as those who have constitutional symptoms.