Although mammograms are the most common method used to find breast cancer, mammography is far from perfect. In fact, it is so far from perfect that it cannot be trusted as a scientifically valid process for breast cancer detection. The following citations indicate the weakness of this approach to detecting, and preventing, breast cancer.
Does mammography save lives? Yes, definitely, but it is not the only approach, and it has significant weaknesses that should encourage women to use a variety of screening methods.
The purpose of this annotated bibliography is to provide evidence that describes the effectiveness of mammograms for finding cancer.
Sensitivity: "…the percentage of breast cancers detected in a given population, when breast cancer is present." Sensitivity is the percentage of cancer cases the technology finds, or how sensitive the test is to cancerous tissue. With a low sensitivity, many cancers are not found, which results in false negatives.
1.0 (100%) sensitivity would mean the technology finds every case of cancer.
0.50 (50%) sensitivity means the technology correctly finds cancer half the time.
False Negative: The results falsely indicate that the test is negative for cancer, meaning it indicates the woman does not have cancer when she actually does. This is the most "dangerous" statistic. A woman may have breast cancer, but the technology doesn't find it. Doctors try to avoid false negatives because they can cause a woman not to seek treatment that she needs.
Specificity is the percentage of screenings that correctly indicate that no cancer is present—how well the test can specify whether the tissue is cancerous or not. With a low specificity, non-cancerous tissue is identified as possible cancer, which results in false positives.
1.0 (100%) specificity means the technology never indicates cancer when there is no cancer.
0.50 (50%) specificity means the technology correctly indicates the absence of cancer half the time.
False Positive: A finding of potential cancer when there is no cancer. The the results falsely indicate that the test for cancer is positive, meaning the test falsely indicates that the woman has symptoms of breast cancer when she actually does not.
Meaning: a mammogram, alone, may not find cancer, particularly in the early growth of cancer, and a single mammogram is not a good indicator of the presence or absence of cancer.
Of the women with non-invasive cancer, mammograms found 78.9% of the cancers, which means the mammogram failed to find 21.1% of cancers. This corresponds with the finding that 1 in 5 cancers are missed.
Mammograms find 79% of cancers, missing 21%, which is about 1 in 5, overall. However, the mammograms find even fewer cancers in younger women and in women with dense breasts at any age.
Researchers found only 0.43 sensitivity with standard mammograms, missing 57% of cancers. Even with the new CEDM approach, they only found 62% of cases, missing 38%. For women with dense breasts, only 35% of cancers were found through standard mammography, increasing to only 59% through the experimental technique.
PPV: Positive Predictive Value, how accurately the screening predicted the existence of cancer.
PPV1: The percentage of suspicious or highly suspicious findings from initial examinations that results in a tissue diagnosis of cancer. Only 4.3% of initial suspicious findings resulted in a diagnosis of cancer. 95.7% of suspicious initial findings were not diagnosed as cancer, which is a very high false positive rate. In the 18–29 age group, 98.17% of initial abnormal findings were not cancer.
PPV2: The percentage of suspicious or highly suspicious findings during follow-up examinations that results in a tissue diagnosis of cancer. Only 25% of suspicious findings from follow-up examinations were diagnosed as cancer. 75% of suspicious findings from follow-up examinations were not cancer, which is also very high false positive rate. In the 18–29 age group, 87.97% of these findings were not cancer.
PPV3: The percentage of known biopsies performed as a result of an examination interpreted as suspicious or highly suggestive of malignancy that results in a tissue diagnosis of cancer within 1 year —based on biopsy findings, only 29% of cases were confirmed to be cancer. The false positive rate based on performed biopsies is 71%, meaning 71% of suspicious or highly suggestive mammogram findings were not cancer. In the 18–29 age group, 86.13% of these findings were not cancer.
The overall conclusion is that mammograms are weak at determining whether or not a woman has breast cancer, leading to many women receiving follow-up examinations, stress and fear, and invasive biopsies that they never needed.
About half of all cancers found by mammograms are not clinically significant but the mammogram findings will lead to potentially harmful treatment anyway.
These are false negatives. For every 100 women with breast cancer, 6 to 46 cancers will be missed. The lower rate reflects findings for older women and the higher rate reflects findings for younger women and women with the special cases listed.
A single mammogram is highly unlikely to cause cancer, but, as noted, the effects are cumulative lifelong. Statistical analysis results in 0.1% of women acquiring breast cancer from mammogram screenings. The U.S. population of women aged 40 to 79 is 67,995,242. Approximately 67% of women in this age range get mammograms, which is 45,556,815 women. If 1 in 1,000 get breast cancer from mammograms, then mammograms may cause 45,557 cases of breast cancer.
With a 5-year breast cancer survival rate of 89.2%, 10.8% do not survive 5 years after the initial diagnosis of cancer. 10.8% of 45,557 means 4,920 women may die from breast cancer caused by mammograms.
Carney PA1, Miglioretti DL, Yankaskas BC, Kerlikowske K, Rosenberg R, Rutter CM, Geller BM, Abraham LA, Taplin SH, Dignan M, Cutter G, Ballard-Barbash R.
Adjusted sensitivity reflects statistical manipulation of the data to remove the effects of other conditions. For example, to determine the effect of breast density, the adjustment factors out the effects of age and hormone replacement therapy. Fatty breasts, which are easiest to screen accurately with mammography only yield a sensitivity of 87%, missing 13% of cancers. Older women are more likely to have an accurate screening, but the sensitivity is still only 83.3%, missing 16.7% of cancers. When the effects of density and age are combined, the sensitivity rates are less, with the lowest sensitivity for younger women with dense breasts.
Effects of age, breast density, ethnicity, and estrogen replacement therapy on screening mammographic sensitivity and cancer stage at diagnosis: review of 183,134 screening mammograms in Albuquerque, New Mexico.
Rosenberg RD1, Hunt WC, Williamson MR, Gilliland FD, Wiest PW, Kelsey CA, Key CR, Linver MN.
Sensitivity is very low for women under 40 years of age, with nearly 1/2 of all cancers not identified, and only 81% identified in the oldest age group. Among women with dense breasts, 32% of cancers were missed, with 15% of cancers missed for the group with the least dense breasts.