37 CFR § 42.208 - Institution of post-grant review.
(a) When instituting post-grant review, the Board may authorize the review to proceed on all or some of the challenged claims and on all or some of the grounds of unpatentability asserted for each claim.
(b) At any time prior to institution of post-grant review, the Board may deny some or all grounds for unpatentability for some or all of the challenged claims. Denial of a ground is a Board decision not to institute post-grant review on that ground.
(c) Sufficient grounds. Post-grant review shall not be instituted for a ground of unpatentability unless the Board decides that the petition supporting the ground would, if unrebutted, demonstrate that it is more likely than not that at least one of the claims challenged in the petition is unpatentable. The Board's decision will take into account a patent owner preliminary response where such a response is filed, including any testimonial evidence, but a genuine issue of material fact created by such testimonial evidence will be viewed in the light most favorable to the petitioner solely for purposes of deciding whether to institute a post-grant review. A petitioner may seek leave to file a reply to the preliminary response in accordance with §§ 42.23 and 42.24(c). Any such request must make a showing of good cause.