Interval cancers following breast cancer screening in Singaporean women

Abstract

Our study reports on the interval cancers arising in the subsequent 3 years in women screened as part of the Singapore Breast Cancer Screening Programme that commenced in 1994. Women, the majority of Chinese ethnicity, were either invited or not invited by random allocation to be screened. All women, other than those identified with breast cancer at screening, whether invited or not, were followed for 3 years, and information on all breast cancers arising in this period was obtained through the national registry. In particular, the cancers arising from those women who were deemed free of the disease at screening were noted. The mammographs taken at screening of those women who developed such an interval cancer were rereviewed by 3 radiologists. In the 28,099 women who were screened and deemed free of disease, 59 interval cancers were reported with annual rates of 2.1, 10.6 and 10.8 per 10,000 womenyears in the succeeding 3-year periods. In 39,425 women who were invited but declined screening, the rates were 17.0, 15.5 and 11.7, while the corresponding rates from 97,294 women not invited were 12.8, 13.3 and 13.0. Whereas the annual incidence at 1 year in women who have been screened is much lower than those in the 2 groups who were not screened, it is of a similar magnitude by 2 years. This suggests that locally an optimal screening interval may be close to 1 year. The rereview of the mammograms of those 59 women with interval cancers suggested that the maximum possible number of these that might have been detected at screening was 10 (17%).

The epidemiology, radiology and biological characteristics of interval breast cancers in population mammography screening

“…MC more common on diagnostic mammograms of FNs than those of true interval BCs (28 vs. 14%). Cases with true interval or FN findings had similar background parenchymal patterns, but those with occult interval BC had higher proportion of dense patterns, p  < 0.05Gao 36 Review of 59 interval BCs (Singapore screening program 1994–97) by three radiologists using index screens; semi-informed (aware reviewing interval cases but unaware of tumour location).Missed/FN: 17% (based on 'worst diagnoses' from five screen-readers, two from initial reads and three from re-review).In 3 years of successive follow-up from index screen, interval BC rates per 10,000 women-years were 2.1, 10.6 and 10.8 each year. BC breast cancer, DM digital mammography, FSM film-screen mammography, FN false-negative, MC micro-calcifications, IC interval cancer, RCT randomised controlled trial a Classification of interval BCs: true interval (cancer is not visible at the index mammographic screen but becomes visible at the diagnostic mammogram); missed/FN (cancer is visible on the index mammogram but is not recalled or is misinterpreted); minimal-signs (subtle abnormality is visible on the index mammogram but one that is unlikely to warrant recall); occult (cancer that is not visible on the index screen and not visible on the diagnostic mammogram) b Semi-informed radiological review generally involved screen-readers knowing that interval BC cases were being reviewed, without information on the side and location of the interval cancer c In some studies 'true interval' BCs are also referred to as 'occult' at the index or pre-diagnosis screen; this should not be confused with the conventional 'occult cancer' classification of interval cases, which usually refers to a BC that is not seen on the index mammography screen and also occult on the diagnostic mammogram d Blinding or blinded methods of review: this generally refers to (a) interval cases being interspersed with screen-reading as part of the routine screening workflow; or (b) interval cases being mixed with normal screening mammograms but not integrated into routine screen-reading workflow (study-specific methods described in table) …”

“…No evidence of an excess of lobular BCs in occult group.–Porter 48 Comparison of 538 interval BCs by radiological type, in a UK screening program service, 1987–2000.True and occult interval BCs (combined) were more likely to be histological grade 3 than minimal-signs and FN cases (52% vs. 35%, p  =  0.05). FNs were more likely to have lobular histology than other interval BCs (47% vs. 20%, p  < 0.001).–Gao 36 Interval vs. screen-detected BCs from Singapore screening program 1994–97; also reported comparison to those declining screening and those not invited to screening.Interval BCs were more likely to be stage II (52.5% vs. 31.1%) and have a tumour size >20 mm than screen-detected BCs, but less likely to be DCIS (10% vs. 26.5%). Distribution of axillary nodal status was similar between screen-detected and interval BCs; however, proportion of high-grade tumours among interval BCs (38%) was higher than screen-detected BCs (18.6%) and was similar to non-screened groups.–

BC breast cancer, ER estrogen receptor, FN false negative, HER2 human epidermal growth factor receptor 2, PR progesterone receptor, OR odds ratio, NPI Nottingham prognostic index, DCIS ductal carcinoma in-situ

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Assessing risk of breast cancer in an ethnically South-East Asia population (results of a multiple ethnic groups study)

“…In order to focus on incident breast cancer, women were included only if they were followed-up to be alive without disease (5 in situ ) for the next 3 years. As the prevalent breast cancers are not included, the study women have a lower absolute risk than the general female population [12]. Thus the 'clock' was started 3 years from the date of their negative screen and, amongst these women, those who developed invasive breast cancer in the following 4-8 year period are the designated cases.…”

Cytology is useful in breast screening: results and long‐term follow‐up of the Singapore Breast Screening Pilot Project

“…A total of 2185 women (8%) were recalled for review: further radiological assessment was performed on 5% of women, 2% underwent joint assessment, and 1% underwent both. Out of the cases recalled, 135 breast cancers were detected in 132 women, which equated to a rate of 4.68 per 1000 women screened 2,4 . A total of 232 women underwent FNAC of the breast during the screening period.…”

“…Out of the cases recalled, 135 breast cancers were detected in 132 women, which equated to a rate of 4.68 per 1000 women screened. 2,4 A total of 232 women underwent FNAC of the breast during the screening period. Clinical assessment and aspiration of palpable lesions by ÔfreehandÕ was performed for 154 cases (66.4%).…”