ACR mammography classification
By Cécile Bour, MD, Radiologist
November 11, 2018
Testimony of the radiologist....
I was alerted by fellow general practitioners who rightly questioned the ACR classification in the conclusions of our mammogram reports, and who tended to draw a parallel between this scale and the seriousness or poor prognosis that their patient would have ...
The question is quite relevant, as we, radiologists happily classify our description in a sort of coded verdict, without really explaining the why and how of things and without realizing that for the correspondent it is not intuitive to know to what these ACRs correspond. Above all, there is a great risk of overlaying this classification of imaging alone with the classification of cancer severity stages.
However, the two have nothing to do with each other.
The ACR classification
ACR (American College of Radiology) classification was developed in 1990, due to the need of systematizing reports in order to harmonize practices. We find 5 stages which correspond to the more or less certainty of having to deal with a cancer in front of a mammographic image.
ACR 1: normal, the breast has " nothing to report ".
ACR 2: we have images that are only benign abnormalities, this includes small axillary nodes, micro cysts, images that are undetermined but have been strictly unchanged for ages, fibro-adenomas or cysts that are already well known and have been identified as benign (by ultrasound, MRI or previous biopsy), vascular, cystic or galactophoric microcalcifications, amorphous glandular islets etc...
ACR 3: this stage designates an image that is not very worrying but whose future is to be verified, which was not known before, or known but has changed slightly compared to previous exams. The standard proposed procedure for this classification is a single monitoring at 6 months, then at one year, to ensure that it does not increase in size or that the analysis criteria do not become more characteristic in favour of malignant lesions.
ACR 4 classification means that there is a high probability of cancer, and that it is a very suspicious abnormality to be sampled in any case. ACR4 therefore automatically implies a biopsy, under ultrasound (micro-biopsy) or under radiographic control, by a mammotome procedure (macro-biopsy), or directly by biopsy-exeresis. In the end, we may have made a misinterpretation, or it may be a poorly evolving cancer, or even a very aggressive cancer; the type of image that led us to classify it as ACR4 says nothing about the aggressiveness or not of the cancer, if what we biopsied is indeed one!
ACR 5: the anomaly is very strongly suspected of malignancy and the semiological criteria are quite evocative and typical of malignancy. We can say that we are very, very sure of the malignancy.
ACR 0 is the incomplete examination that will have to be added to other imaging examinations.
This description of the mammographic image determines the decision
Unfortunately, on the one hand it is very subjective. Not all "expert" readers always agree on whether to classify as ACR 3 or ACR 4.The switch from analog to digital mammography (a recent process which, I intentionally shorten and simplify, makes you see better and smaller things than the previous mammography process) makes it more complicated to compare an old exam done in analog to a "better" digital imaging.This will give the impression of an image with perhaps more irregular contours than before, or which would be denser, or slightly increased in volume, whereas it is simply the change in technique that induces this doubt, as the images of two different examinations are not strictly overlapping.
On the other hand, medico-legal issues have become more prevalent over time, as well as the increase of the overall level of anxiety for both the patients and the medical profession. The ACR3 classification is more and more abandoned in favor of the ACR4 which becomes an abominable bottomless pit into which the radiologist throws almost any image that does not let him sleep.
As we have already seen on this site neither the specificity nor the positive predictive value of mammography are good.
Specificity is the probability that the screening mammogram will be negative for a subject (in this case the screened woman) who is not ill. However, the specificity of screening mammography is not sufficient, because the test may be positive in some cases when the woman is not ill.
Unfortunately, the double reading, practiced for the organized screening in France, presented as an improvement of the screening test, further decreases the already poor specificity of the mammogram, and at the slightest doubt the second reader will outperform the mammogram for fear of "missing" a cancer. In other words, the already poor specificity of screening mammography is further weakened by double reading.
The positive predictive value is the probability that the subject (the woman being screened) will be ill for a positive test. The PPV of screening mammography is very low, between 9 and 10%.
This means that for a woman for whom the mammogram is judged positive and for whom a biopsy of the incriminated image is performed, there is a 90% chance (100%-10% of PPV) that the biopsy will come back negative and therefore has been excessively proposed. As the journal Prescrire has pointed out, breast biopsies have literally exploded since the screening was performed. 
In practice, it is important to remember that radiological classification has nothing to do with the classification of cancerous stages, and that an ACR4 classification is not always based on a very dubious radiological semiology, but to a large extent because we want to identify the cancer by sampling very quickly, because a new image that was not visible before has appeared, because an image may have changed or become a little bigger, because one does not want to give oneself the time to simply monitor, any diagnosis becoming abusively urgent and intolerable in the minds of professionals as well as the public. Contrary to what is taught to the public, there is no urgency or loss of chance to wait a few weeks, a few months... But this reasonable and wait-and-see attitude is no longer possible nowadays, especially after alarming public appearances of health authority officials or opinion leaders alerting people by the press or popular health programs that "we have no time to lose".
The level of anxiety in the population, already very high because the multiplication of these invasive gestures, misunderstood because they are poorly justified, it will further become even higher.
What makes us wonder is that in the new European MyPEBS trial, initiated to study the relevance of stratified screening based on risk, the fact of having had a biopsy, even a benign one, represents a risk factor for women that justifies classifying them as « being at higher risk than normal »...
See page 19/20 of the synopsis: https://cancer-rose.fr/my-pebs/wp-content/uploads/2019/12/MyPEBS-Protocol-.V1.2-du-27.07.18-.pdf
Well, being a woman is already a big risk...
 Prescrire magazine, February 2015/Tome 35 N°376