Parenchymal pattern in women with dense breasts. Variation with age and impact on screening outcomes: observations from a UK screening programme

Laura Ward, S. Heller, S. Hudson, L. Wilkinson

To assess patterns of parenchymal tissue on mammography in women with dense breasts and to determine how this varies with age and affects recall to assessment and cancer diagnosis. Breast density data was obtained in women attending routine mammographic screening from April 2013 to March 2015 using automated breast density assessment software. Women with the densest breasts were selected for visual interpretation of parenchymal pattern (PP). One hundred non-assessed women, aged 50, 55, 60, 65 and 69-71 years (total = 500), provided controls. Cases included women recalled for assessment (mastectomy or implants excluded) (total = 280). Mammograms reviewed by ten readers and PP classified as: (1) very smooth; (2) mainly smooth; (3) mixed; (4) mainly nodular; (5) very nodular. The ratio of women in each category at each age and screening outcomes were compared by Pearson's chi-squared test. Reader agreement for scoring PP was good (intraclass correlation = 0.6302). Proportions of women in each PP category were similar at all ages for controls (p = 0.147) and cases (p = 0.657). The ratio of PP categories did not vary significantly with age in those who underwent biopsy (p = 0.484). Thirty-four cancers were diagnosed. There was a significant correlation between a diagnosis of cancer and nodular PP compared to not nodular PP (p = 0.043). The ratio of smooth to nodular pattern in women with the densest breasts did not vary with age. The PP of the breast tissue did not affect likelihood of recall to assessment or biopsy. There was a significant relationship between a nodular parenchymal pattern and diagnosis of cancer. • This paper shows that there is good agreement between mammogram readers when classifying mammographic PP on a five-point scale from very smooth to very nodular. • In non-assessed women with the densest breasts, there is no significant change in the proportions of smooth to nodular patterns with increasing age. • The likelihood of recall for further assessment or biopsy at assessment is not related to PP in women with highest breast density. • When recalled for further assessment, significantly more women are diagnosed with cancer in the group with nodular PP on mammography when compared with smooth and mixed patterns.