"Simple blood test" – cancer breakthrough or nightmare?

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tzleft.welch_gilbert_courtesy.jpgThat’s the question Dartmouth’s Dr. Gil Welch asks in a column on the CNN website.

He reflect on last week’s news about a test in development that might find a single cancer cell among a billion healthy ones – as so many news stories framed it.

Welch analyzes:

“But it’s not that simple. The test could just as easily start a cancer epidemic.

Most assume there are no downsides to looking for things to be wrong. But the truth is that early diagnosis is a double-edged sword. While it has the potential to help some, it always has a hidden side-effect: overdiagnosis, the detection of abnormalities that are not destined to ever bother people in their lifetime.

Becoming a patient unnecessarily has real human costs. There’s the anxiety of being told you are somehow not healthy. There’s the problem that getting a diagnosis may affect your ability to get health insurance. There are the headaches of renewing prescriptions, scheduling appointments and keeping them. Finally, there are the physical harms of treatments that cannot help (because there is nothing to fix): drug side-effects, surgical complications and even death. Not to mention it can bankrupt you.

Americans don’t need more diagnoses, they need the right diagnoses.

I don’t know whether this test will help some patients. It might, but it will take years to figure that out.

But I do know that the test will lead more people to be told they have cancer (or that their cancer has returned). That will lead more people to receive cancer treatment. Because these new patients are bound to be less severely ill (if they are ill at all), they will appear to do better. Many will assume that their doing better is because of the new test and early treatment. So the test will be performed more often. And a lot of money will be made along the way.

Ironically, what this test might actually teach us is that it’s not that unusual for healthy people to have an occasional cancer cell in their blood.”

Coincidentally, a urologist’s editorial in this week’s Journal of the American Medical Association discusses a study on treatment for men’s urinary incontinence following prostate cancer surgery. And this leads him to reflect on overtreatment as well. Excerpt:

“In the era of prostate-specific antigen (PSA) screening, the overdiagnosis rate of clinically indolent prostate cancer (defined as a screen-detected cancer that would not present clinically during the patient’s lifetime) is estimated to vary between 23% and 42%. A patient with this type of low-risk cancer, therefore, is exposed to the adverse effects of aggressive interventions, such as surgery or radiation, with little or no benefit. Several publications have documented the feasibility and safety of active surveillance, which consists of PSA testing and serial prostate biopsies and delay of aggressive therapy until the patient meets prespecified pathologic or biochemical thresholds. It is time that patients with prostate cancer and their physicians consider this option more seriously.

Clearly, many factors discourage the increased use of active surveillance, including patients’, family members’, and clinicians’ preconceived notions about cancer in general and prostate cancer specifically and financial incentives that encourage the use of aggressive intervention in this disease. While these obstacles may be difficult to overcome, it is important that clinicians rethink existing treatment approaches if the goal is reducing the incidence of complications–such as urinary incontinence–associated with treatment of localized prostate cancer.”

Comments (4)

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Gregory D. Pawelski

January 12, 2011 at 1:47 pm

My comment is not really about early cancer diagnosis. It is about prognostication and drug selection with the CTC (circulating tumor cells) technique. The number of cells discovered in the CTC technique has turned out to be a good prognosticator of how well treatments are working. Monitoring CTCs could be utilized for confirmation after the patient is administered either empiric or assay-directed most beneficial therapeutic agents.
But CTCs really aren’t useful with respect to drug selection. The problem is with isolating (even by size) and analying single cancer cells. The supposition is that common cancers can be detected and cured through analysis at a genetic level of a small number of cells or even a single wayward cell. CTCs are free-floating cancer cells that can remain in isolation from a tumor for over twenty years.
And what is the relationship of such long-lasting cells to the tumor cells that needed to be attacked through tested substances? And in regards to some molecular tests utilizing living cells, generally of individual cancer cells in suspension, sometimes derived from tumors and sometimes derived from CTCs, this was tried with the old human clonogenic assay, which had been discredited long ago.
One testing approach to find CTCs actually can miscount non-tumor epithelial cells as tumor cells. And also highly invasive cells may not be detected if you are looking for epithelial antigens because the CTC also goes through a phase called “epithelial to mesenchymal transition”, where you will miss locating that tumor cell if you are targeting the antigen.
The key is to look for the tumor cell and not something else that “hangs with the tumor cell.”

Elaine Schattner, MD

January 12, 2011 at 3:13 pm

I think Dr. Welch missed the point (as did others) of this technology. It was developed, primarily, to help oncologists monitor tumors in patients who already are known to have disease. For example, doctors could check for new, resistance-conferring mutations in patients who are already on a cocktail of meds for lung cancer.
The blood test could obviate the need for repeatedly doing CT scans and biopsies to measure disease the extent of disease and new mutations in people undergoing cancer treatment. So the investment, by J&J – which was what the news was about – makes it more likely this will actually happen in non-research clinics. The technology has the potential to make cancer patients’ lives easier and less costly, and for doctors to stop giving them meds to which they’ve acquired resistance.
I should mention I did write on this a while back (@SciAm: http://bit.ly/ekzXvQ). – Elaine