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

The relationship between tumour size, malignancy grade and dense mammographic parenchymal patterns was evaluated by using a nested case-control design with 875 breast cancer cases and 2 601 matched controls. Wolfe's classification was used to assess mammographic parenchymal patterns. The dense P2/DY mammographic parenchymal patterns were significantly associated with invasive ductal grade 3 carcinoma (OR = 2.03; 95%, CI 1.13-3.62, p = 0.016). Stratified by tumour size, we found that the odds ratio for grade 3 invasive ductal NOS breast cancer measuring 15-19 mm associated with P2/DY mammographic parenchymal patterns was 3.46 (95% CI 1.12-10.68). For tumours larger than 30 mm, the odds ratio was 10.09 (95% CI 1.27-79.93). The highest risk of grade 3 cancers being in tumours measuring 30 mm + may be due to dedifferentiation of missed cancers, but there is some excess even in the < 20 mm tumours, suggesting an increased risk in association with dense mammographic patterns of some aggressive cancers which are grade 3 at inception. Our results are consistent with the model that breast cancer is a progressive disease, whose development can be arrested by screening, and that the point at which individual tumour progression is stopped is crucial for prognosis not simply in terms of stage of disease, but also of histological grade.