Inter Partes Review
A party may request an inter partes review to challenge the validity of an issued patent. To date, about 77% of all patent claims that have been reviewed have been found to be invalid. An inter partes review is conducted by the Patent Trial and Appeals Board (PTAB).
The inter partes review has two stages, an institution stage and a trial stage. During the institution stage, the PTAB determines if there is a resonable likelihood that the petitioner would prevail" on at least one of the challenged claims. If the challenge is sufficient to warrant a trial, the PTAB conducts the full trial on the merits.
Claims may be amended during inter partes review, although this right is limited.