A medical student adds the fluorescent dye bromodeoxyuridine (BRDU) to four cell samples isolated from both healthy and diseased patients. BRDU is a synthetic analog of thymidine. After treating the cells for 48 hours with BRDU, she examines the number of fluorescent cells in each sample. In a healthy tissue, 10% of cells are typically BRDU+ after 48 hours of treatment. She finds the results below.
Given the description of BRDU and the results presented in the figure, what might BRDU be a marker for?