Submitted by Dr.Kattlove’s Cancer Blog

Every so often, a doctor would refer me a patient who had widespread cancer without any warning signs or symptoms. Usually, we could diagnose the origin of the cancer – lung, pancreas, testicle, stomach were often the likely sites. The cancer would start in these organs and then quickly spread throughout the body without any tip off. There it was!

But sometimes, we were unable to figure out where the cancer started. These cancers are called “cancers of unknown primary”. We don’t know how often these occur, because no one keeps statistics on these. I would probably see one or two patients with this diagnosis each year. Usually, treatment wasn’t effective and they would die in a short space of time. Most publications say that about 2-5% of all cancers fall into this category. I suspect it is lower. As our diagnostic imaging tools have improved, we are able to pin down the origin of some of these.

At one time, I predicted that genetic tests would pinpoint the origin of more of these cancers. Now I think that time has come. Researchers from Israel have found that a small gene associated molecule called “micro RNA” can tip us off to the origin of widespread cancers. Micro RNA is a new player in the genetics game. It has only been known about for a few years. It functions as a control valve for genes and plays a role in turning them on or off.

The Israeli researchers found that each type of cancer has a specific set of micro RNAs that can distinguish them from others. By checking a cancer’s line of micro RNAs, they were able to call the origin of cancers in most patients with widespread cancer. These were patients where the origin of the cancer was known, but not to the researchers.

Will this help? Probably. In the past, we would try to guess where the cancer started. If they had cancer in lymph nodes in the chest and abdomen and were males, the cancer might be related to testicular cancer and would often improve with chemotherapy designed for testicular cancer. If the cancer was in lymph nodes under a woman’s arm, then breast cancer was the likely diagnoses. If they were a big time smokers with cancer all over, we would think of lung cancer. Then we would treat with chemotherapy based on our guess.

The problem with this approach is that the chemotherapy was often ineffective and, because we had guessed wrong, patients had to put up with all the side effects of chemotherapy while they were dying of this very fatal disease. So now if we know where the cancer started, we can better tailor our treatment. Will this help? Perhaps a little. The major advantage of knowing the diagnosis is that if we know what cancer we are dealing with and if it doesn’t respond to the chemotherapy appropriate for that cancer, we can lay off and concentrate on keeping the patient comfortable during their last months.

No great breakthroughs for these unfortunate people, but at least a possible measure of comfort.

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