Is There a Breast Cancer Risk Despite a Negative Mammogram?

Mammography is widely used worldwide for early breast cancer diagnosis as a cancer screening procedure. Mainly thanks to mammography and increased awareness, most breast cancers are diagnosed early, and 5-year survival, expressing complete cancer treatment, has reached %90 across all breast cancer stages today. Nevertheless, even with a negative or benign mammography result, women retain some breast cancer risk. 

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Results of a notable study on breast cancer risk after a negative mammogram were published in July 2018 in JAMA Oncologyas the journal.

Study details

• The study enrolled, between 2011-2014, screening mammography patients older than 40, totaling 306 thousand women without a previous breast cancer diagnosis.
• In the study, poor-risk/prognosis breast cancer was defined as:
  • distant organ metastasis,
  • regional lymph node involvement,
  • hormone-positive HER 2-negative breast cancer with a tumor larger than 2 cm,
  • larger than 1 cm, triple-negative breast cancer or
  • larger than 1 cm, HER2-positive breast cancer.

Study results

• Of the 306.028 women analyzed, 272.881 had negative mammograms. Among these 272 thousand women, during 1 year of follow-up, 160 developed breast cancer (90 with a good prognosis and 70 with a poor prognosis). Thus, within 1 year after a negative mammogram, breast cancer risk was % 0.05 (in 10 thousand, 5 cases) as found. 
• Poor-prognosis breast cancer accounted for % 26.9 among women with positive mammograms versus % 43.8 with negative mammograms, a statistically significant difference.
• Among all women with negative mammograms, those with dense breastshad 2 times higher breast cancer risk.
• Neither age nor family history was significantly associated with cancer diagnosis after a negative screening mammogram.
• Among women with negative mammograms, younger women had a 3.5-fold higher risk of poor prognosis. Neither breast density nor family history was associated with poor prognosis in these women.
• Among women with positive mammograms, breast density was not associated with breast cancer diagnosis. However, age and family history were associated with risk in this group (risk increased with age and a family history of breast cancer).

- Related topic: What Are Dense Breasts? Why Is Cancer Risk Higher?

Commentary

Breast cancer risk after a negative mammogram is very small (per 10 thousand negative results, 5 cancers). Mammography therefore remains an effective early-detection screening tool. Cancers arising after negative mammography have a slightly higher poor-prognosis risk. Dense breasts are the most important factor increasing cancer risk after a negative mammogram, but in this study density did not mean worse prognosis. Women with dense breast tissue should be followed with breast ultrasound (USG) alongside mammography. 

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