Objectives: To investigate the hypothesis that interval cancers arising soon after the previous screen and true interval cancers are biologically aggressive and have a relatively poor prognosis compared with other interval cancers, and to assess which prognostic features are relevant to interval cancers.
Methods: Analysis of prognostic pathological features (grade, lymph node stage, size, vascular invasion, oestrogen receptor [ER] status and histological type), radiological features (comedo/non-comedo calcification and spiculation) and survival for 538 invasive interval breast cancer cases by type and time since previous screen.
Results: Late interval cancers were less likely to be lymph node positive (13 versus 43%, P = 0.003). Type 1 interval cancers were more likely to be histological grade 3 than type 2 (minimal signs) and type 3 (false-negative) intervals (52 versus 35%, P = 0.05). Type 3 interval cancers were more likely to have lobular features than other intervals (47 versus 20%, P < 0.0001). There was no significant survival difference by interval cancer type (P = 0.64) or interval year (P = 0.83). At univariate analysis of all interval cancers, tumour size, grade, nodal stage, ER status, vascular invasion and comedo calcification were associated with survival. On multivariate analysis of prognostic features significant at univariate analysis, nodal stage (P value = 0.009), tumour size (P = 0.001), ER status (P < 0.0001) and vascular invasion (P < 0.0001) maintained independent significance.
Conclusions: Our study shows that true intervals and interval cancers arising quickly after screening do not have a worse prognosis than other interval cancers, and that interval cancers have a unique set of prognostic features.
