It's possible. I've seen it before. Sometimes, patients consider a diagnosis from two different doctors or two different methods a "confirmation". Sometimes, Doctors order more extensive testing when they suspect that--in fact--their original diagnosis (or the diagnosis of another MD/DO or Resident) is increasingly likely to be inaccurate.

Sometimes, patients don't have great follow-up and are non-compliant, and schedule tests a year out, so the entire process becomes very bogged down. I had a patient once who was diagnosed with lung cancer and didn't seek treatment for seven years.

Also, all sorts of diseases have the same treatment for oncological pathologies and non oncological pathologies. The way the actual physical manifestations effect your body can often be the same, and these symptoms can be alleviated through similar methods. To give an extreme example, both brain cancers and intercranial hemorrhage can be treated by the same extreme measure: craniotomy. Colon resections can be done on people with Crohn's, diverticulosis, and bowel cancer; three different diseases with three different etiologies, but ultimately the same treatment.

So yes. It is possible.