Table 3.

Summary of study cohorts in BIG 1-98 trial

Population	N	Description
Randomized patients	8028	Total patients enrolled in BIG 1-98.
Intention-to-treat patients	8010	Eighteen randomized patients withdrew consent to participate before starting treatment.
Two-arm randomization option	1828
Four-arm randomization option	6182
Safety population of PCA	7963	Excludes 47 patients from the ITT population who received no study treatment. This population is used for reporting all adverse events.
Primary core analysis (PCA)	8010	Follow-up for two sequential treatment groups is censored at the date of the switch + 30 days. Maximizes the number of patients and events in head-to-head comparison of L vs T. Gives more weight to early events.
Monotherapy cohort	4922	Patients randomized to receive 5 years of tamoxifen alone or letrozole alone.
Two-arm randomization option	1828	Provides additional events with longer follow-up. More appropriate for direct comparison of intended 5-year longer-term use of each agent as monotherapy.
Four-arm randomization option	3094
Four-arm cohort from randomization	6182	Patients in the ITT population enrolled in the four-arm randomization option to compare treatment strategies from the time of randomization.
Four-arm cohort from switch (approximately 2 years from randomization)	5828	Patients enrolled in four-arm randomization option, who were alive and disease-free 30 days after the fifth drug pack was dispensed (approximately 2 years and 1 month after randomization). Used to assess the value of starting with one agent and switching to the other compared with remaining on the original agent.
Central pathology assessment cohort	6291	Total number of patients with at least one of four markers (ER, PgR, HER-2, Ki-67) assessable through retrospective, central pathology review.
Monotherapy cohort	3650