Study Background: Eight hundred consecutive women under age 50 at who had been diagnosed with stage 1 or 2 breast cancer HER2+ in the past year and received either trastuzumab or a new drug, L01FD07, were enrolled in an observational cohort for 5-year follow up. Two hundred and sixteen patients received trastuzumab, and 584 patients received L01FD07. Although it was not the primary outcome of interest, over the course of follow-up there were 20 participants whose breast cancer progressed to stage 4 (metastatic), and the investigators would like to examine this finding more closely. Of the 20 cases of metastatic progression, 9 occurred among patients who received trastuzumab and 11 occurred among patients who received L01FD07.

Note: trastuzumab is the current standard of care for HER2+ breast cancer, and L01FD07 is made up for the purpose of this exercise.

a. Use the information provided to fill in the number of individuals with and without metastatic progression over the 5 years of follow-up in Table 2 (left blue box). Are metastatic progressions incident or prevalent values?

b. For all patients, calculate and interpret the 5-year risk of a metastatic progression per 100 patients with HER2+ breast cancer. Add this measure of occurrence to Table 2 (green box "Total" row). Round your answer to 2 decimal places.

c. Calculate and interpret the 5-year risk of a metastatic progression per 100 persons with HER2+ breast cancer who receive trastuzumab. Repeat this calculation for those who receive L01FD07. Add these measures of occurrence to Table 2 (green box). Round your answers to 2 decimal places. Show all work. (Though not required, it may help to use the 2x2 table provided).

Table 2. Risks and rates of metastatic progression over 5 years by treatment type among 800 patients with stage 1 or 2 HER2+ breast cancer

	Metastatic Progression	No Metastatic Progression	Person-years	5-year risk per 100 patients	Rate per 1000 PY
Trastuzumab			980
L01FD07			2840
Total			3820