Patients, insurance companies, and doctors generally like it when generic forms of medicines become available as they are less expensive than the brand name medicines.  And small molecule drugs can be made as generics once the patent expires.  For biologics (which includes monoclonal antibodies and vaccines) it is not so straightforward.  Even after the patent expires, these are difficult to make because in general they are difficult to make.  The originator has not just the patent as protection but also the trade secret of how the drug is made.  (Even by the standards of pricey medicines, biologics are expensive, and they account for most of Medicare’s spending on prescription drugs.)

Enter biosimilars.  These are not exact copies of the original medicine, but they act in the same manner in the body.  Regulatory agencies will approve medicines that have been shown to have the same efficacy in the body.  Like generics, biosimilars tend to be less expensive than the original medicine, but still not inexpensive.

The seller can use any brand name they choose, but the generic or scientific name is dictated by the regulatory agency.  The name for biosimilars is the same as the name of the source biologic product but appended with four letters.  These four letters have no special meaning, but are just meant to differentiate among the biosimilars and to indicate the original drug the biologic is duplicating.

As of mid 2022, the US FDA has approved 37 biosimilar drugs.  While most are for arthritis treatment, some are approved for cancer therapy:

Other terms for biosimilars are biogenerics or follow-on biologics.