What the letter grade on a cancer-screening recommendation actually means

Behind almost every US cancer-screening recommendation is a single letter: A, B, C, D or I. The grades come from the US Preventive Services Task Force, an independent volunteer panel, and they are easy to misread as a report card, where A is good and D is bad. They are not that. They encode two different things at once — how confident the evidence lets the panel be, and whether the balance of benefit and harm favours screening at all — and understanding the difference explains a lot of the confusion about what people "should" be screened for.

The grades, in the panel's own words

The clearest way to read the ladder is through actual recommendations. Colorectal cancer screening happens to span three grades at once, which makes it a useful key.

An A means high certainty of substantial net benefit. The Task Force gives colorectal screening for adults aged 50 to 75 an A recommendation, concluding with high certainty that it has substantial net benefit [s1]. A B means the benefit is a step lower — moderate net benefit, or high certainty of moderate benefit. Screening adults aged 45 to 49 for colorectal cancer is a B [s1], as is annual low-dose CT lung screening for eligible smokers, which the panel judged to have a moderate net benefit in a high-risk group [s2]. A and B are the grades that mean "do this."

A C is where it gets counterintuitive. It does not mean "don't." It means the net benefit across everyone in the group is small, so the service should be offered selectively based on individual circumstances. Colorectal screening for adults aged 76 to 85 who have been screened before is a C: whether to continue should weigh the person's overall health, prior screening and preferences [s1].

A D does mean don't. It signals moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits. Screening the general population for pancreatic cancer is a D — the panel found the potential benefits do not outweigh the potential harms [s3].

The grade that is not a verdict at all

The odd one out is I, for insufficient evidence. An I statement means the evidence is inadequate to weigh benefits against harms, so the panel cannot make a recommendation either way. Screening asymptomatic people for skin cancer with a whole-body visual exam is an I statement [s4]. This is the most misunderstood grade: it is not a recommendation against screening, and it is not a green light. It is a declaration that the studies needed to decide have not been done — which is a statement about the state of research, not about the individual in front of a doctor.

Why the certainty and the benefit are separate axes

The reason a single letter can feel slippery is that it compresses two judgments. One is how strong the evidence is — the certainty. The other is which way the benefit-harm balance tips. A D and an I can both mean "not recommended for routine use," but for opposite reasons: a D rests on good evidence that screening does not help, while an I rests on a lack of good evidence at all. Treating them as the same thing — or treating either as proof that screening is worthless — misses the point of the system.

Why the letters carry money

In the United States, the grades are not merely advisory. Coverage of preventive services was expanded under the Affordable Care Act in a way tied to Task Force recommendations, and the practical effect is measurable. A study of nearly 250,000 screening mammograms found that new Task Force practice recommendations were associated with decreased screening among younger and older women, while insurance-coverage changes under the Affordable Care Act were associated with increased screening among women aged 50 to 74 [s5]. In other words, the grade a service receives can shift how many people actually get it — which is why the grades are argued over as fiercely as the underlying science.

What this means for a reader

A screening recommendation's letter grade is a compact summary of a careful judgment, not a ranking of importance. A and B mean the evidence supports screening; C means offer it selectively; D means the evidence points against routine screening; and I means the evidence cannot yet say. None of these is a substitute for a personal conversation, because the grades describe populations, and an individual's risk, age and history determine how a given recommendation applies to them. Knowing what the letter means, though, makes it far easier to understand why guidelines say what they say — and why they sometimes disagree.

Sources

• [s1] Screening for Colorectal Cancer: USPSTF Recommendation Statement, JAMA, 2021-05-18
• [s2] Screening for Lung Cancer: USPSTF Recommendation Statement, JAMA, 2021-03-09
• [s3] Screening for Pancreatic Cancer: USPSTF Reaffirmation Recommendation Statement, JAMA, 2019-08-06
• [s4] Screening for Skin Cancer: USPSTF Recommendation Statement, JAMA, 2023-04-01
• [s5] Mammography Screening Following the USPSTF Recommendations and the Affordable Care Act, PLOS ONE, 2015-06-29