The detection of ductal carcinoma in situ at mammographic screening enables the diagnosis of small, grade 3 invasive tumours.

This study was carried out to assess the frequency of ductal carcinoma in situ (DCIS) occurring within and surrounding grade 3 invasive tumours and the effect of its detection on size and nodal stage of invasive carcinomas at mammographic detection. Grade 3 tumours with either no associated DCIS or DCIS only within the invasive component were significantly larger in size than tumours with surrounding DCIS (P < 0.02) and were less likely to be under or equal to 10 mm in size (0% or 13% vs 30% respectively, P < 0.02). Tumours with mammographic calcification were more likely to be less than or equal to 10 mm in size than non-calcific tumours (32% vs 11% respectively, P < 0.05). This was because of the high frequency of tumours less than or equal to 10 mm in size in the linear/branching calcification group. Tumours showing calcification without a mass also appear to be a group with good prognostic features, with a mean size of 13 mm, 33% being 10 mm or less in size and only 17% being node positive. We have found that the presence of surrounding DCIS enables earlier detection of grade 3 invasive carcinomas because of the presence of mammographically visible calcification. Detection of calcification suggestive of DCIS should remain an important part of mammographic screening.