The state of cancer research is a frequent topic on this blog (for example, here, here and here), so this NY Times excerpt from Columbia oncologist Siddhartha Mukherjee’s new book – Emperor of All Maladies: A Biography of Cancer (Scribner November 16, 2010) – caught my eye. It’s well worth a read:
Why does cancer relapse? . . . when a cancer disappears on a CT scan or becomes otherwise undetectable, we genuinely begin to believe that the disappearance is real, or even permanent, even though statistical reasoning might suggest the opposite. A resurrection implies a previous burial. Cancer’s “relapse” thus implies a belief that the disease was once truly dead.
But what if my patient’s cancer had never actually died, despite its invisibility on all scans and tests? . . .
In fact, this view of cancer – as tenaciously persistent and able to regenerate after apparently disappearing – has come to occupy the very center of cancer biology. Intriguingly, for some cancers, this regenerative power appears to be driven by a specific cell type lurking within the cancer that is capable of dormancy, growth and infinite regeneration – a cancer “stem cell.” [. . .]
But if tumors contain dedicated stem cells, then delivering maximal doses of poisons to kill the bulk of the tumor might achieve one response – a shrinkage of the tumor – but have no effect on relapse. If the rare stem cell lurking within a tumor somehow escapes death, then it will reassert itself and grow again. Cancers will come back like a garden that has been cleared by hacking at its weeds while leaving the roots behind. [. . .]
If such a phoenix-like cell truly exists within cancer, the implication for cancer therapy will be enormous: this cell might be the ultimate determinant of relapse. For decades, scientists have wondered if the efforts to treat certain cancers have stalled because we haven’t yet found the right kind of drug. But the notion that cancers contain stem cells might radically redirect our efforts to develop anticancer drugs. Is it possible that the quest to treat cancer has also stalled because we haven’t even found the right kind of cell?
It isn’t necessary to posit stem cells. Mere statistics will do. Imagine you have a tiny cancer with ten million cells, and your treatment is 99.999% effective (that is, it kills 99.999% of cancer cells). That leaves 100 living cancer cells, far too small to detect on any scan but plenty for relapse.
If you do the math, you will see that a cancer that doubles every 30 days is inevitably lethal because it will be back to full size in a couple of years, and your body can only take a few rounds of chemo/radiation in such a short span of time before the treatment starts killing you faster than it helps you. On the other hand, a cancer that takes so long to double that it (for example) starts at 30 and is detectable at 60 (many breast cancers are like that) means that you are overwhelmingly likely to be dead of something else (like mere age) before the cancer is again detectable at 90.
Your life expectancy here had nothing much to do with the treatment or how soon the cancer was detected. That’s why breast cancer mortality has improved little even though we’ve spent billions on early detection and treatment.
Interesting thoughts to ponder, especially for those of us who have the “Big C”. More worrisome is that for folks with blood cancers, the numbers are so amazingly large that the concept of “killing” the cancer with an external modality is ultimately a futile effort. I’m very excited about the concept of gene/immunotherapy in which the body is actually taught to recognize the cancer as alien and do something about it. Reprogramming or re-aligning stem cells to create new/better/functional sentries…