Interval breast cancer
Interval breast cancer is a term given to cancers detected/presenting within 12 months after a mammographic screening in which findings are considered normal 2. The term is a statistical benchmark used in conjunction with other parameters to assess the efficacy of breast imaging programmes and the statistics of mammogram readers. It is a strong indicator of how successful your screening programme is.
The definition is potentially confusing because the implication suggests that an imaging error was made and also because interval cancers appear on the statistics of the most recent previous mammogram reader, by convention. The fact is that true negative interval cancers actually developed in the time period between the last mammogram (read as "normal") and the one on which the cancer was detected.
Interval cancers might be divided into a number of categories:
- true negative interval cancer: no sign of disease may be detected on previous screening mammogram; the lesion is new.
- interpreted as benign interval cancer: a lesion that proves to be malignant showed benign morphological characteristics on the previous mammogram.
- retrospectively visible interval cancer: a now known lesion is seen on the previous screen mammogram; this is an interpretive error on the part of the reader.
- single reader interval cancer: a second reader would have discovered the lesion. second reads in screening programmes yield up to 10% more cancers.
- technical failure interval cancer: a technically poor image hampered the reader to discover the abnormality; in theory suboptimal images will not be submitted for interpretation and if they are, should not be read.
The review of interval cancers is an integral, essential part of the QA process in any breast imaging programme. It is time consuming but like pathology review, yields benefits for the whole programme. These are cases where careful objective review gives valuable insights and opportunities to learn and improve the whole programme from the image acquisition through to interpretation.
Interval cancer rates are defined parameters in most programmes and the recommended rates vary depending on the country. The rates are higher where the screening interval recommended is longer (i.e. where mammograms are recommended every 3 years as opposed to every year).
This value cannot be seen as a stand alone parameter when assessing the efficacy of a programme or its workers. It is only a single value that needs to be seen in the context of all the other statistical values used in the assessment. On its own it has no value.
Interestingly, most interval cancers are found in patients 50-54 years old.
- 1. Hofvind S, Skaane P, Vitak B et-al. Influence of review design on percentages of missed interval breast cancers: retrospective study of interval cancers in a population-based screening program. Radiology. 2005;237 (2): 437-43. doi:10.1148/radiol.2372041174 - Pubmed citation
- 2. Burhenne HJ, Burhenne LW, Goldberg F et-al. Interval breast cancers in the Screening Mammography Program of British Columbia: analysis and classification. AJR Am J Roentgenol. 1994;162 (5): 1067-71. AJR Am J Roentgenol (abstract) - Pubmed citation