“Targeted therapy.” It’s the holy grail of cancer research these days. If you listen to its most vocal proponents, it’s the path towards “personalized medicine” that improves survival with much lower toxicity. With the advent of the revolution in genomics that has transformed cancer research over the last decade, including the petabytes of sequence and gene expression data that pour out of universities and research institutes, the promise of one day being able to a patient’s tumor, determining the specific derangements in genome and gene expression that drive its uncontrolled proliferation, and finding drugs to target these abnormalities seems more tantalizingly close than ever. Indeed, it seems so close that even dubious practitioners, such as Stanislaw Burzynski, have jumped on the bandwagon, co-opting the terms used by real oncologists and real cancer researchers to sell “personalized gene-targeted cancer therapy,” which in their hands are really no more than a parody of efforts to synthesize the enormous quantity of genomic data each patient’s tumor possesses and figure out how best to take advantage of it, a “personalized genomic therapy for dummies,” if you will.
That’s not to say that there aren’t roadblocks to realizing this vision. The problems to be overcome are substantial, and I’ve discussed them multiple times before. For example, just a couple of weeks ago I discussed an example of just what it takes to apply these new genomic techniques to an individual patient. The resources required are staggering, and, more problematic, there often aren’t any single “magic bullet” molecular pathways identified that can be targeted with existing drugs. The case I discussed was a fortunate man indeed in that such a pathway was identified, but most tumors are driven by many derangements in growth control, metabolism, migration, and the other hallmarks of malignancy described by Robert Weinberg. Worse, in many cases we don’t even have drugs that can attack many of the abnormalities that drive cancer progression. Then there’s the issue of tumor heterogeneity, which comes about because cancer is as good example of a disease as I can think of in which evolution due to natural selection results in incredible differences in the cancer cells in one part of the tumor compared to other parts of the tumor or in the tumor metastases. A “targeted” therapy that targets the genetic abnormalities in one part of the cancer might well fail to target the genetic abnormalities driving another part of the tumor.