the boston globe ran a story earlier this month pointing out the marginal benefit of mammography from a recent analysis –see below, but they had a thoughtful summary (see here)
the article came out in JAMA (see doi:10.1001/jama.2014.1398) and reinforces the not-so-great efficacy of mammog screening, confirming what i posted in several blogs. they did literature search finding 8 large RCTs (all done between the 1960s and 1990s, which may be an issue: see below) finding a 15-20% decreased breast cancer mortality. another meta-anal from canadian task force found 19% decrease after 11.4 yrs of followup. the new JAMA data (see tables below) includes the relative risk (RR), absolute risk reduction (ARR), overdiagnosis (detected tumors on screening that would never become clinically evident. mostly DCIS, but some suggestion that may also be some invasive cancer diagnoses). this article is available for free, so i am reproducing their results below.
table 1: pooled results from RCTs on mortality reductions with mammog screening by age group
| Age | Total events in group/total number Mammog grp Control grp | RR with mammog |
ARR with mammog | Number needed to screen | |
| 39-49 | 448/152300 | 625/195919 | 0.85 (0.75-0.96) | 0.0005 | 1904 |
| 50-59 | 361/78465 | 410/69849 | 0.86 (0.75-0.99) | 0.0007 | 1339 |
| 60-69 | 110/19093 | 155/18377 | 0.68 (0.54-0.87) | 0.0027 | 377 |
| 70-74 | 42/5073 | 36/4859 | 1.12 (0.73-1.72 | NA | NA |
table 2: estimated benefits and harms of mammog screening in 10,000 women with annual mammog over 10 year period
| Age | # Diagnosed with invasive unnecessary breast ca or DCIS over 10 yrs | # Breast ca deaths in next 15 yrs | # Deaths averted with screen over next 15 yrs | Overdiagnosis during 10 yrs | # With >=1 false pos during 10 yrs | # With >=1 biopsy during 10 yrs |
| 40 | 190 | 27-32 | 1-16 | ?-104 | 6130 | 700 |
| 50 | 302 | 56-64 | 3-32 | 30-137 | 6130 | 940 |
| 60 | 438 | 87-97 | 5-49 | 64-194 | 4970 | 980 |
(note: the “# of breast ca deaths in next 15 yrs” column is the number who would die even if they were screened)
they point out that these studies were of women of average risk and the benefit would likely be greater if women at higher risk. for example 4 microsimulation (ie mathematical) models found that women 40-49 with Gail model score twice average and given biennial screen would have same ratio of benefit/harm as woman>50 with average risk.
so, this is a very complex issue. this article confirms the pretty paltry benefits of mammography screening (although average lifetime risk of breast cancer is 12.3%, aggressive mammog screening will avoid breast cancer mortality in only 3-32 of 10,000 women screened in their 50’s, with 6130 having false positives, 940 getting biopsies, 30-137 with overdiagnosed breast cancers) and does not include the fact that treatment is much better now than when the studies were done, and does not even mention that all these mammograms are likely (by mathematical modeling) to create some cancers. also important to note that the differences in breast cancer mortality do not translate into differences in all-cause mortality (prob in part because the numbers saved by mammog is really so small). attempts at provider/patient shared-decision-making so far have probably not been adequate (eg, no change in mammog ordering after USPSTF came out with guidelines to decrease mammogs to every other year and only in women 50-74. also, boston globe comments on 2010 study of 460 women, where >96% reported that MD discussed benefits of screening but <20% discussed risks). be aware that the suggestion of doing individualized risks, esp those 40-50 yo, (Gail model etc) makes sense mathematically, but there are no real-world data. also that the array of imputed breast cancer risk factors (inc BMI, dec bone density, smoking, alcohol, estrogen/androgen exposure, late age of first pregnancy…) are absent in 60% of women with breast cancer. which also (again) raises the elephant-in-the-room: the huge numbers of industrial toxins in our environment, food chain, water… which may well be a really major cause of breast cancer (the vast vast majority never adequately tested, but we do know of many so far which have hormonal stimulatory effects on breast tissue). but in the context of mammog, i think it makes sense to discourage women under 50 from getting mammog, and doing mammog every 2 year in women aged 50-74 (there are pretty good data that every other year testing is just about as sensitive and fewer false positives… and also less radiation)
geoff