Heisenberg uncertainty principle: A principle in quantum mechanics holding that increasing the accuracy of measurement of one observable quantity increases the uncertainty with which another conjugate quantity may be known.
Perhaps it is because I just got back from Albuquerque, a city which has become like a second home to me, that I have Heisenberg on my mind. For the one or two of you out there who are not Breaking Bad fans, “Heisenberg” is the name that mild mannered chemistry teacher Walter White assumes when he decides to manufacture pharmaceutical quality methamphetamine after being diagnosed with Stage III lung cancer. His motivation is to be able to leave his pregnant wife and son affected by cerebral palsy a little cash when he dies. The evolution of Walter from upstanding high school teacher to ruthless drug lord unfolds over six seasons where moral ambiguity is the coin of the realm — in uncertainty principle terms, the more single-mindedly he pursues his meth business, the fuzzier his personal ethics become.
Recently I have begun to think of the dilemma of PSA testing and the diagnosis and progression of prostate cancer in terms of the Heisenberg uncertainty principle. Nowhere is this more apparent than in the case of men who have a rising PSA level post-prostatectomy. For many men faced with the choice of surgery versus radiation therapy, the selection revolves around the perception of certainty.
In medical school we are given the mantra, “To cut is to cure!” Many patients choose surgery because of that perception — the ability of the surgeon after the procedure to say, “We got it all,” and the satisfying thud of that post op PSA falling to zero. Life is as it should be, the offending organ is gone, and the PSA is the definitive proof of cure.
In my own career I have pointed out countless times that if a man wants it black and white, cut and dried as it were, he may be more satisfied with the surgical option, since the slow fall in the PSA level post radiation therapy, with its attendant subtle blips and variations can be maddening to the patient, his family, and of course the attending physician.
But what of the patient whose PSA post-prostatectomy does not fall to an undetectable level? Or the patient whose PSA becomes unmeasurable, but months or years later starts to rise again? On the one hand, our ability to measure serum PSA levels as a proxy for prostate cancer still lurking in the body has improved to the point of being able to measure values as small as hundredths of a nanogram per milliliter of blood. We call this the supersensitive PSA assay and we accept this as proof that the cancer is there, somewhere, waiting to recur.
But what this supersensitive test cannot tell us is exactly where those cancer cells are. Neither bone scan, nor CT scan, nor ProstaScint imaging nor ultrasound is likely to give us the answer. So what do we do? As radiation oncologists we offer the patient the best we have, treatment to the “prostate bed” — the area where the prostate used to be — and sometimes the adjacent lymph nodes. We know statistically that over a period of years, large groups of patients who were treated for their rising PSA with radiation do better than those who were not, but sadly this tells us nothing about the individual patient. And the individual must decide for himself whether to take the leap of faith, and the side effects of one treatment compounded with another, that the cancer cells are still localized and that the radiation will kill them.
As a clinician treating patients with rising PSAs post-prostatectomy, I wait with bated breath for the first PSA after radiation to the prostate bed. The patient is equally anxious — that stark simple but highly precise number is the measure by which we judge success or failure of the treatment. But in focusing on the PSA, we often forget the obvious — that a number, even a highly precise number, is just that and nothing more. What the patient will die from, and when, remains uncertain. If I can help my patients remember that, and go and live their life with zest and satisfaction, then I have done them a real service.
Miranda Fielding is a radiation oncologist who blogs at The Crab Diaries.