Mammographic parenchymal patterns and breast cancer natural history - A case-control study

The relationship between tumour size, malignancy grade and dense mammograph ic parenchymal patterns was evaluated by using a nested case-control design with 875 breast cancer cases and 2 601 matched controls. Wolfe's classific ation was used to assess mammographic parenchymal patterns. The dense P2/DY mammographic parenchymal patterns were significantly associated with invas ive ductal grade 3 carcinoma (OR = 2.03; 95% CI 1.13-3.62; p = 0.016). Stra tified by tumour size, we found that the odds ratio for grade 3 invasive du ctal NOS breast cancer measuring 15-19 min associated with P2/DY mammograph ic parenchymal patterns was 3.46 (95% CI 1.12-10.68). For tumours larger th an 30 mm, the odds ratio was 10.09 (95% Cl 1.27-79.93). The highest risk of grade 3 cancers being in tumours measuring 30 min + may be due to dediffer entiation of missed cancers, but there is some excess even in the < 20 mm t umours, suggesting an increased risk in association with dense mammographic patterns of some aggressive cancers which are grade 3 at inception. Our re sults are consistent with the model that breast cancer is a progressive dis ease, whose development can be arrested by screening, and that the point at which individual tumour progression is stopped is crucial for prognosis no t simply in terms of stage of disease, but also of histological grade.