Figure 1.

Biologic manufacturing includes multiple steps that may vary between manufacturers, potentially leading to differences between a biosimilar and its reference product that cannot be fully characterized with available analytical methods. In contrast, small-molecule drugs are manufactured through chemical reactions that can be reliably reproduced to make identical copies (generics) that can be fully characterized. Used with permission from Mellstedt H, Niederwieser D, Ludwig H. The challenge of biosimilars. Ann Oncol. 2008;19:412.