Which blood test results would most indicate further testing for cancer?

Question

As a member of the healthcare community, I've long been taught (as we have all) that test results are only valid in the context of symptoms and at the discretion of a healthcare professional.

That being said, preventative medicine has long suffered at the hands of treatment-based medicine, and at present the cost of routinely conducting tests for the most dangerous of medical conditions is prohibitive for most. In the interest of promoting preventative medicine, what if routine, inexpensive blood tests were used as a prescreening for further condition-specific testing, rather than strictly as an accompaniment to patient complaints of symptoms?

To zero in on one common and dangerous category of conditions in particular, which test results in common blood tests (CBC, CMP, etc.) would most indicate, with high sensitivity and irrespective of symptoms or whether the patient is even experiencing symptoms yet, further testing for potential cancer cases?

Answer 1

Short answer? Most likely none.

Better answer? What you are asking is what we health professionals call "Screening tests", which are by definition highly sensitive but relatively non-specific routine tests that are cost-effective to conduct routinely in HEALTHY population at risk for a particular disease.

Things like Prostate Antigen or Occult Blood in Stool may fall in this category.

So, there won't be a catch-all for what you want. Especially because "cancer" is, as you probably know, not a disease but rather a cluster of them, with different epidemiologies.

For example, it makes sense to check PSA in a male over 40 years of age, as screening for prostate cancer, because it is a slow disease with very good prognosis if caught early.

Same PSA, same pathology, but now your patient is a man identical to the first example, except he is now 80 years old. It is in fact much more probable that you will get an altered result and that he will in fact have prostate cancer. However, it's pretty futile to check his PSA because even if it was through the roof and he did in fact have cancer, at that age the benefit of actually making the diagnosis and treating him more likely than not will be outweighed by the cost of treatment (speaking both in terms of money and quality of life).

In short. Yes, there are such a thing as screening tests. Yes, they are great tools if employed judiciously. No, there are no catch-all batteries of tests that could detect cancer in healthy individuals in a cost-effective way.