Interval Cancers

The detectable preclinical phase, also known as the sojourn time, is the estimated duration of time that an occult tumor can be detected before the onset of symptoms .

In a screening program, the lead time is the amount of time before the expected onset of symptoms actually gained by screening.

The breast cancer sojourn time will vary somewhat in individuals due to personal characteristics and tumor histology, but in the context of screening programs, the analysis of the randomized controlled trial (RCT) data has shown that the mean sojourn time (MST) and mean lead time primarily vary by age.

Estimates of the MST vary in the literature and with method of calculation, but a consistent finding is that the breast cancer MST is not very long and lengthens with increasing age.

Estimates of the MST range between 2.0 to 2.4 years in women aged 40 to 49, 2.5 to 3.7 years in women aged 50 to 59, and 3.5 to 4.2 years in women aged 60 to 69, and approximately 4.0 to 4.1 years in women 70 to 74.

Knowledge of the MST is important for determining screening intervals in a breast cancer screening program.

The sojourn time defines the upper limit of the lead time that might be gained and thus should provide most individuals undergoing regular screening with the opportunity to detect occult disease while still localized .

When a screening interval exceeds the MST, there is increased potential for a higher rate of interval cancers

Interval cancers are cancers that present with symptoms in the interscreening interval, thus with poorer prognosis in that subset of incident cases.

Early evidence of the influence of MST on the interval cancer rate was seen in the Swedish Two-County study, which reported nearly twice the interval cancer rate in women aged 40 to 49 compared with women aged 50 and older when both groups were screened at intervals of 24 or more months.