The cancer called “unknown”

Every so often – maybe once a year – I would see a patient who had widespread cancer yet I had no clue about where the cancer started. In spite of CT scans and other tests, I would come up empty handed. No obvious source was found. These cancers would be called cancers of unknown primary.

Because these cancers were widespread, they were mainly incurable although there were some exceptions. In spite of their poor outlook, they might be helped by some kind of drug treatment like chemotherapy. But, I needed to know which drugs would be most effective and this depended on the kind of cancer it was. My first step would be to take the biopsy specimen from one of the metastatic sites to the smartest pathologist I knew and ask him to venture an educated guess. If it made sense, I would use that “guess” to tailor my treatment.

If my pathologist friend was stumped, then I would try to guess the origin of the cancer from the clinical picture. For example, young men with a tumor in the middle of their chest could have what we call a germ cell tumor. Testicular cancer is an example of this although the cancer doesn’t need to arise there. These are highly treatable, even curable with the right chemotherapy. I would treat these guys with the drugs that work for germ cell cancers. When it worked, it was like a miracle.

Sometimes all the cancer was in lymph nodes; then I could guess it was a lymphoma, which is also a highly treatable and often curable cancer. I remember an elderly woman with enlarged lymph nodes that my pathologist friend guessed was a lymphoma. I treated her for this cancer and her tumors melted away. But after a couple of treatments, she didn’t want any more. I kept seeing her though for a couple of years afterwards and her cancer never came back. She was either very lucky or knew her body better than I did.

If the patient was a woman and had a tumor near the breast, I would treat her as if she had breast cancer – also a cancer that responds well to chemotherapy and hormonal treatments. If the patient was a heavy smoker and didn’t fall into any of these categories, I would assume the cancer came from the lung, which would discourage me from any aggressive treatment. Another typical source of these cancers was the pancreas or stomach. Neither of these cancers would be helped much by treatment.

At one time, about 5 percent of all widespread cancers would fall into this category of unknown primary. Now as new tests have come on board, the percent has fallen. It may even be much smaller with the advent of a new test for these tumors that relies on their genetic composition. Recent studies have shown that looking at the genetic makeup of the cancer cells can identify about 90 percent of the cancers. But this can be an expensive proposition that may not be covered by insurers. The good news is that Medicare just said it would pay for it so it is likely that most insurers will fall into line and also pay for it.

The problem is that even if we know the diagnosis, unless it is a germ cell tumor or lymphoma or maybe breast cancer, we re still stuck. None of the rest of the possibilities will have much of a benefit from chemotherapy. Maybe the patients will get a couple of months of remission, but much more is unlikely.