In a previous note, I launched a discussion about cancer overdiagnosis (see: Confusion Caused by Conflating "False Positive" and "Overdiagnosis" in Breast Cancer). Here's an excerpt from that note:
Overdiagnosis, in my opinion, is very different [from a false positive test]. The various stages of the development of breast cancer constitute a spectrum of disease from a lesion that shows the earliest signs of malignancy to one in which the cells are highly atypical under the microscope and represent an aggressive lesion. One type of overdiagnosis can occur if and when a pathologist tilts in his or her judgment toward a slightly more malignant interpretation on this continuum. This may not be an error on the part of him or her but may rest within the range of correct diagnoses....The diagnostic criteria may be broad or the experts may not totally agree about them. However, there is yet another form of overdiagnosis based on the biologic nature of the cancer. Into this category falls those lesions referred to above as "better off not being found." In such cases, for example, all pathologists diagnosing such the lesion might agree that it shows similar morphological criteria of malignancy. However, the lesion may not possess the genes programming it to invade and metastasize in vivo....Lesions of this type should not be biopsied at all because they could lead to the "pure harm" referred to above. Unfortunately and at this time. we don't have a means to determine a priori which breast masses not to biopsy because any diagnosis would constitute overdiagnosis and any treatment would be overtreatment.
We have now teased out two types of cancer overdiagnosis by a pathologist: (1) lesions where he or she tilts toward a more malignant lesion by training or judgment but remains in the correct range of diagnoses; and (2) lesions that look malignant under the microscope but are not genetically programmed to behave in an aggressive fashion in-vivo. A recent article suggested yet another category (see: Colitis patients' cancer tests may lead to excessive treatment). Below is an excerpt from it:
Screening for colon cancer in patients with chronic colitis has never been more sensitive. But advanced screening methods...are leading physicians to question the standard treatment options that includes surgical removal of the entire colon, a procedure that can worsen a healthy patient's quality of life. That's according to results of a study led by gastroenterologist Dr. Peter Higgins, assistant professor in the Department of Internal Medicine [at the University of Michigan Medical Schoool]. The study appears in the November edition of GUT....Patients with ulcerative colitis and Crohn's colitis, inflammatory bowel diseases that cause chronic inflammation of the digestive tract, are at increased risk of colon cancer, and the standard of care requires regular colonoscopy for surveillance every one to two years. For these cases, the traditional screening method is to collect random biopsies throughout the colon via a colonoscope to look for the presence of pre-cancer (dysplasia) in colon cells....But advanced endoscopic methods have made it possible for doctors to identify with much more sensitivity very early, small areas of pre-cancerous cells. The identification of these cells is not based on chance, and is not influenced by size or area. These cells are less likely to be associated with invasive cancer, and it may not be appropriate to surgically remove the colon if pre-cancerous cells are found with these sensitive methods.
Here we have an example of patients with chronic colitis who are predisposed to develop cancer of the colon by the development of dysplastic patches of mucosa. Advanced endoscopic methods now permit monitoring and identification of smaller areas of altered cells that might have gone undetected in prior times. These is no quibble here about the judgment of the pathologist. It's a case of the gastroenterologist perhaps being too vigilant and efficient in providing samples of dysplastic tissue to the pathologist because of more sophisticated screening methods. So we now have a third type of overdiagnosis to add to our list, this one attributable to clinicians: (3) more efficient clinical surveillance and monitoring methods leading to earlier detection of disease and perhaps premature life-altering treatment.
Similar problem with melanoma screening, reviewed in the November 2009 issue of British Journal of Dermatology.
http://www.ncbi.nlm.nih.gov/pubmed/19785614
Posted by: Martin Trotter | December 03, 2009 at 12:14 PM