Few Losses to Follow-Up in a Sub-Saharan African Cancer Cohort via Active mHealth Follow-Up: the Prospective ABC-DO Breast Cancer Cohort.

: Accurate survival estimates are needed to guide cancer control efforts in sub-Saharan Africa, but previous studies were hampered by unknown biases due to excessive losses-to-follow-up (LTFU). In the African Breast Cancer-Disparities in Outcomes prospective breast cancer cohort, we implemented active mHealth follow-up, phoning each woman, or her next-of-kin (NOK), trimonthly on her mobile phone to update her vital status. Dates of every contact with women/NOK were analysed from diagnosis in 2014-2017 to the earliest of 1st September 2018, death or 3-years post-diagnosis. The cumulative incidence of being LTFU was calculated considering deaths as competing events. In all, 1490 women were followed for a median of 24.2 (inter-quartile range (IQR) 14.1-34.5) months, corresponding to 8571 (66% of total contacts) successful contacts with the woman/NOK. Median time between successful contacts was 3.0 (IQR 3.0-3.7) months. In all, 71 women (5.3%) were LTFU at three years: 0.8% in Nigeria, 2.2% in Namibia, 5.6% in Uganda and, due to temporary discontinuity of active follow-up, 20.3% after two years in Zambia. The median time to study notification of a death was 9.1 weeks (IQR 3.9-14). Although the present study was not a randomized controlled trial, in this cancer cohort with active mHealth follow-up, LTFU were much lower than in previous studies and enabled estimation of up-to-date and reliable cancer survival.