“Just optimize it.”

Examiners often rely on routine optimization to do a lot of work in an obviousness rejection, and a recent PTAB decision illustrates one way to push back when you claim the destination and the prior art merely provides directions. In other words, knowing which direction to go is not necessarily enough to know where to stop.

In Appeal 2026-001617, Application 17/535,969, the claims were directed to a cysteine and methionine deprivation diet for cancer treatment. Claim 3 included numerous numerical limitations, including 18–65 mg of iron per daily serving, 0–10% saturated fatty acids, and a PUFA-to-MUFA ratio of at least 2:1.

The Examiner relied on 10 (ten!) references to assemble the claimed formulation. For several of the numerical limitations, however, the Examiner did not identify a prior-art disclosure of the claimed value or range. Instead, the Examiner relied on teachings that certain ingredients should be increased or decreased. The Examiner then invoked optimization. The Examiner’s rationale may seem reasonable on first glance – the prior art says to increase something, so it would be obvious to do so and that would take you toward your claimed range.

The Board was not persuaded, and provides the sage quote that “… a reason to move the dose in a particular direction does not provide a sufficient reason to stop within the specific claimed range.”

The problem was not necessarily that the prior art failed to provide a reason to make a change. The problem was that the Examiner did not explain why following that direction would lead to the particular numerical ranges recited in the claims, including understanding both the start point (from which to move) and the end point (at which to stop moving). For example, the prior art suggested increasing iron, but one of the cited references did not disclose any dietary iron amount. The only dietary iron quantity identified by the Board was 9 mg in another reference, which did not overlap the claimed 18–65 mg range. Similarly, the prior art suggested favoring polyunsaturated fatty acids over monounsaturated fatty acids. But the Examiner identified no ratio that would lead to the claimed PUFA-to-MUFA ratio of at least 2:1. And for saturated fatty acids, the prior art suggested minimizing them. According to the Board, however, “[a] direction to minimize is not a disclosure of the claimed ceiling” of about 8–10%.

These distinctions illustrate an important limit on an examiner’s ability to rely on routine optimization to fill in missing disclosure in the cited art. Consider the more conventional optimization situation addressed in MPEP § 2144.05. There, for example, the prior art may disclose a range from which a skilled artisan could determine an optimum or workable subrange through routine experimentation. The MPEP also explains that an examiner relying on routine optimization must provide an articulated rationale explaining why it would have been routine to arrive at the claimed invention.

That was the problem here. The Examiner provided directions, but did not identify the destination. The Board ultimately held that the applied art did not teach or suggest the claimed limitations.

When the Examiner relies on a teaching to increase or decrease a parameter, don’t stop at asking whether the prior art provides a reason to make that change. Ask the next question, as to why would the skilled artisan have stopped at the claimed value or within the claimed range. If the rejection does not answer that question supported by evidence in the record, the applicant may have identified an important gap in the obviousness analysis.

Of course, this does not mean that an examiner must always find the exact claimed endpoint in a single reference. Prior art can provide a range, multiple references can collectively provide a range, and other evidence can provide a reason to select a particular value. Nor does the Board’s decision eliminate the established law concerning routine optimization.

So, when responding to a routine-optimization rejection, see if you can do more than simply argue that the prior art does not disclose the claimed endpoint. Identify what the Examiner says the skilled artisan would have optimized, what starting point or range the artisan would have used, and what evidence would have caused the artisan to stop at the claimed endpoint. If the Examiner’s reasoning amounts to nothing more than “the prior art says to increase X” or “the prior art says to minimize Y,” point out that the rejection establishes a direction of travel, but does not establish the destination. The burden is not necessarily to show that the artisan could have reached the claimed range; the important question is why the artisan would have arrived there.