American humorist Will Rogers once stated that in the 1930s, “When the Okies left Oklahoma and moved to California, they raised the average intelligence level in both states.”
This quote, though obviously swathed with wit and sarcasm, has surprising applicability to several real world scenarios. The Will Rogers Phenomenon is used to explain what happens when the movement of an element from one set to another set raises the average values of both sets.
The Will Rogers Phenomenon is extrapolated to describe an observation in medicine called stage migration. In simplest terms, stage migration occurs when improved detection of disease leads to patients being reclassified from “healthy” to “unhealthy.”
For any given patient, disease may be present, but if we’re unable to identify it, patients will erroneously be classified as “negative” or “healthy.” Increasing the sensitivity of a diagnostic test allows doctors to capture disease at an earlier stage. Therefore it’s possible to reclassify a previously “healthy” patient as “unhealthy” simply by running a “superior” test. That patient would therefore “migrate” from a healthy group to an unhealthy group because of improved detection of disease.
An important consideration is that despite migrating, nothing has changed about the patient itself. Its true prognosis was previously determined before any test was done. The new test simply allowed for better detection of their disease status.
As an example, I can answer the question of “Did my pet’s cancer spread to its lungs?” by recommending radiographs (x-rays) or a CT scan of the patient’s chest. CT scans will pick up on tumors that are only a few millimeters in size, whereas radiographs will only find lesions that are closer to a centimeter.
If the same patient underwent radiographs and a CT scan, it’s possible the former test could return negative for spread and the latter test could return positive. If we’d only done radiographs, I would offer that owner a better prognosis than if I’d done the CT scan. I would characterize that patient as “healthy” when it truly was “unhealthy.”
Patients diagnosed with more advanced disease are generally not expected to live as long as their truly healthy counterparts. Therefore, “migration” of a newly detected “unhealthy” patient from the healthy group would cause an increase in the average survival time of the healthy group.
Likewise, the migrated patients are generally healthier than the patients previously segregated to the unhealthy group because their disease is considered “less noticeable.” Therefore, their movement to the unhealthy group will increase the average lifespan of that population as well.
Regardless of whether early detection of disease results in an actual difference in patient outcome, the average survival times of both the healthy and unhealthy groups are increased. The Will Rogers Effect holds true!
Stage migration pertains to many aspect of medicine, but there’s distinctive applicability to the discipline of oncology.
Cancer patients are assigned a particular stage of disease depending on where in their body the disease can be detected. For most cancers, stage is predictive of survival. The higher the stage of disease, the more advanced the cancer, and the shorter the anticipated survival time.
Many pet owners are concerned with determining what stage of cancer their dog or cat has without fully understanding what the term stage means or what information it provides.
In order to accurately assign a stage to a pet with cancer, veterinary oncologists must perform all of the recommended staging tests. For example, complete staging for dogs diagnosed with lymphoma includes a complete blood count with pathology review of a blood smear, serum chemistry panel, urinalysis, three view thoracic radiographs, abdominal ultrasound, biopsy of affected tissue, immunohistochemistry for phenotyping purposes, and bone marrow aspirate cytology.
Though I recommend complete staging for all pets diagnosed with lymphoma, very few owners agree to this plan. Further complicating the decision is that although stage is an important predictor of outcome; it generally doesn’t influence the initial treatment recommendations.
Factors such as finances, perception of what the pet will “go through” in terms of testing, timing, and availability of resources all influence whether a pet will have full versus partial staging.
Many patients have some of the tests performed, but it’s rare that they will have all of them done. This means that I’m often making educated guesses about a patient’s stage, and therefore their expected prognosis.
Stage migration is a useful tool to remind doctors to consider every patient as its own separate entity. Generalizations are helpful; however, they do not predict what will happen specifically to your pet.
An open and honest dialogue is the best way to understand what tests your pet needs and what information the results will provide.
This reminds me of another one of Will Rogers’s best quotes: “If there are no dogs in Heaven, then when I die I want to go where they went.”