Interval cancer incidence and episode sensitivity in the Norrbotten Mammography Screening Programme, Sweden

Abstract

Objectives To estimate the interval cancer incidence, its determinants and the episode sensitivity in the Norrbotten Mammography Screening Programme (NMSP). Setting Since 1989, women aged 40 -74 years (n ¼ 55,000) have been invited to biennial screening by the NMSP, Norrbotten county, Sweden. Methods Data on 1047 invasive breast cancers from six screening rounds of the NMSP (1989 -2002) were collected. We estimated the invasive interval cancer rates, rate ratios and the episode sensitivity using the detection and incidence methods. A linear Poisson-model was used to analyse association between interval cancer incidence and sensitivity. Results 768 screen-detected and 279 interval cancer cases were identified. The rate ratio of interval cancer decreased with age. The 50 -59 year age group showed the highest rate ratio (RR ¼ 0.52, 95% CI 0.41 -0.65) and the 70-74 year age group the lowest (RR ¼ 0.23, 95% CI 0.15 -0.36). The rate ratios for the early (0 -12 months) and late (13-24 months) interval cancers were similar (RR ¼ 0.18, 95% CI 0.15 -0.22 and 0.20, 95% CI 0.17-0.24). There was a significantly lower interval cancer incidence in the prevalence round as compared with the incidence rounds. According to the detection method the episode sensitivity increased with age from 57% in the age group 40 -49 years to 84% in the age group 70 -74 years. The corresponding figures for the incidence method were 50% and 77%, respectively. Conclusion Our study showed an interval cancer incidence of 38% and the episode sensitivity of 62 -73%, depending on the method of calculation. Our results are of clinically acceptable level and concert with the reference values of the European guidelines.

Locally advanced breast cancers are more likely to present as Interval Cancers: results from the I-SPY 1 TRIAL (CALGB 150007/150012, ACRIN 6657, InterSPORE Trial)

“…The finding that younger women are most at risk for ICs has been consistent throughout the literature, even when tumor growth rate and disease prognosis have not [22, 23]. In a large, population-based study in Norrbotten, Sweden, the frequency of interval cancers based on age was calculated, demonstrating that ICs were far more frequent in the younger age group (<50 years) [9]. However, in the I-SPY 1 cohort, even after adjusting for age, the actual rate of ICs (85%) for women presenting with a large, rapidly growing tumor far exceeded the expected rate of 32%.…”

“…Using the expected frequency of ICs as reported by the Norrbotten screening program in Sweden [9] and adjusting for age, we would expect a 32.5% interval cancer rate in the I-SPY TRIAL; however, the observed rate is much higher than expected, (57 cases observed vs. 21.7 cases expected, P < 0.001) (Table 4). …”

“…In the large screening trials in Sweden, when the screening interval was defined as 24 months [4–6], the rate of ICs is approximately 17%. IC rates vary by age and may be as high as 43% [8, 9] in younger age groups. The bulk of the data support the conclusion that ICs, compared with their screen-detected counterparts, are rapidly growing (higher grade and larger size), more aggressive (higher frequency of nodal metastases), and more frequently present in younger women [8, 10–12].…”

Interval Cancers in Nasopharyngeal Carcinoma Screening: Comparing Two Screening Intervals after a Negative Initial Screening Result

“…These cancers are inevitable in a cancer screening programme, but their numbers should be kept as low as possible in order to avoid decreasing the screening efficacy. 22 The incidence rate of interval cancer may shed light on the appropriateness of a screening interval. 14 Our results showed that the risk of NPC was 57% lower in the short interval centre, and 53% lower during the first four years in the long interval centre, compared with the general population, but there was no difference during the remaining years in the long interval centre compared with the general population in Sihui.…”

Breast Cancer Screening Program in Lithuania: Interval Cancers and Program Sensitivity After 7 Years of Mammography Screening

“…Interval cancers are inevitable in any screening program, but their number should be kept as low as possible, in order not to decrease the effectiveness of the program. 3 …”