I have been a bit concerned for some time regarding the hype surrounding “personalized medicine” as it relates to cancer. The concern arises from the excitement generated when a novel mutation can be targeted in a specific subgroup of cancer patients with astonishing results. The media goes wild. A good example of this is the BRAF mutation in melanoma. The V600E mutation found in 40-60% of patients with melanoma can be targeted with a drug (vemurafenib) that inhibits this activated cancer causing enzyme. The results can be astonishing, including apparently complete remissions in a disease that only 5 years ago was always fatal when metastatic. However, less well “advertised” is the fact that in most cases, the duration of such responses is quite short (median time to progression with BRAF inhibitors seems to be in the 6 month range). You can read a nice article on this story here. The personalized medicine aspect is that there is no reason to treat with the expensive drug if you don’t find the mutation. That’s the good news of personalized medicine. The bad news is that for cancer, heterogeneity is the achilles heel of this approach. If even one cell doesn’t have the target, it will survive…and/or cells that do have the target have enough genetic instability to get around the block in short order.
Now comes a fascinating study from the outstanding Hopkins investigators who looked at prostate cancer in a single patient who was diagnosed with prostate cancer at age 47. In the beginning he had a lymph node that was involved and he received surgery, androgen ablation, localized radiation and eventually chemotherapy and vaccine therapy. He succumbed to widespread metastases 17 years later at age 64. By doing deep genetic analysis of the primary tumor, the researchers were able to identify the source of the metastases. Surprisingly, the lethal metastatic disease originated in a small part of the primary tumor that was low grade, Gleason pattern 3, not the more aggressive, larger volume tumor elsewhere. While this is the first such study I am aware of in prostate cancer,similar studies in a few patients with renal cancer were reported last year.
So, for personalized medicine, the situation is either a cup half-full or half-empty. If you are an optimist, you hope that the majority of cancer cells in a patient can be targeted with a “driver mutation” like the BRAF mutation, and that when all of the susceptible cells have died off, the immune system might be stimulated to take over with a vaccine, or one of the exciting drugs that potentiate an immune response by knocking down the control arm of the immune system (PD-1 inhibitors, ipilumimab, etc.) and that the last cell will be eliminated before genetic instability gives the cancer the upper hand. If you are on the “half-empty” side, you contemplate that the human genome has evolved over millions of years to be remarkably adaptable to everything from volcano sulfuric gases to solar radiation, and that without such adaptability we might not be here at all. In this scenario, it seems unlikely that we will easily conquer the myriad of survival pathways that got us here by just attacking one of them. And…which one to attack may depend on which biopsy site you look at.
I haven’t decided which philosophic point of view I favor. The incredible progress made in treating HIV by attacking multiple pathways and converting HIV-AIDS to a chronic illness, much like diabetes, provides hope. So does the fact that the Hopkins patient lived 17 years thanks to the progress made in treating prostate cancer. As I often remind my patients, “if you die of a heart attack, we will count that as a cure of your prostate cancer”. May we all live in a healthy condition until our time comes!