Combining large proteins with linkers and cytotoxins, antibody–drug conjugates (ADCs) may be the most complex drug molecules in development today. Despite early promise and product approvals, a number of technical concerns arose during product and process development. Characterizing and ensuring consistency in the number of small molecules that attach to the antibody — as well as ensuring their proper attachment and biophysics — all present significant challenges to ADC developers. Solving early problems associated with product quality has introduced a…