Amgen Inc. v. Coherus Biosciences Inc., 931 F.3d 1154

Background

Amgen’s U.S. Patent No. 8,273,707 claims a process to increase the dynamic capacity of hydrophobic interaction chromatography (HIC) columns by using one of three specific two‑salt combinations (citrate/sulfate, citrate/acetate, sulfate/acetate) at 0.1–1.0 M each.
During prosecution the examiner rejected the claims as obvious over Holtz, which disclosed salts for HIC but not the claimed salt combinations or an increase in dynamic capacity.
Amgen responded, distinguishing Holtz by asserting (a) Holtz does not teach combinations of salts, (b) Holtz does not teach the particular combinations claimed, and (c) Holtz does not teach use of combinations to increase dynamic capacity. Amgen submitted a declaration emphasizing the claimed "particular" salt pairs and their benefits.
The patent issued after continued prosecution. Later, Coherus sought FDA approval for a biosimilar and disclosed a manufacturing buffer containing a salt combination different from Amgen’s three claimed pairs.
Amgen sued Coherus for infringement under the doctrine of equivalents; Coherus moved to dismiss under Rule 12(b)(6). The district court dismissed, holding Amgen clearly and unmistakably surrendered unclaimed salt combinations during prosecution (argument‑based prosecution history estoppel).
The Federal Circuit affirmed, concluding Amgen’s prosecution statements and declaration surrendered claim scope for other salt combinations, barring reliance on equivalents; the court did not reach Amgen’s alternative argument about dedication to the public.

Issues

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether prosecution history estoppel bars Amgen from asserting infringement under the doctrine of equivalents for salt combinations not literally claimed	Amgen: its prosecution distinctions focused on Holtz’s lack of teaching of increased dynamic capacity and any salt combinations generally; references to "particular combinations" were descriptive, not a surrender of other combinations	Coherus: Amgen repeatedly and clearly distinguished Holtz by pointing to the "particular combinations" it claimed, thereby surrendering unclaimed salt pairs	Held: Estoppel applies—Amgen clearly and unmistakably surrendered other salt combinations, so doctrine of equivalents is barred
Whether only the final prosecution submission controls argument‑based estoppel	Amgen: estoppel should be based on arguments in the last response before allowance	Coherus: earlier clear prosecution statements can create estoppel even if not repeated in the last submission	Held: Earlier clear statements can create estoppel; no requirement that only the final submission controls
Whether separate prosecution arguments create separate estoppels	Amgen: multiple grounds to distinguish prior art should be read together, not create separate surrender	Coherus: separate, independent distinctions can each create estoppels	Held: Separate bases can create separate estoppels so long as they were not combined to make a single distinguishing rationale
Whether district court erred in dismissing on estoppel grounds at Rule 12(b)(6) stage	Amgen: factual inferences should be resolved in its favor; estoppel inappropriate on the pleadings	Coherus: prosecution history is part of the record and Amgen’s own filings show clear surrender	Held: Dismissal affirmed—prosecution record shows clear and unmistakable surrender as a matter of law

Key Cases Cited

Trading Techs. Int’l v. Open E Cry, LLC, 728 F.3d 1309 (Fed. Cir. 2013) (prosecution history estoppel bars recapture of surrendered subject matter by equivalents)
Conoco, Inc. v. Energy & Envtl. Int’l, L.C., 460 F.3d 1349 (Fed. Cir. 2006) (describing amendment‑ and argument‑based estoppel and the required clear and unmistakable surrender)
Deering Precision Instruments, LLC v. Vector Distribution Sys., Inc., 347 F.3d 1314 (Fed. Cir. 2003) (standard for argument‑based estoppel requiring clear surrender)
PODS, Inc. v. Porta Stor, Inc., 484 F.3d 1359 (Fed. Cir. 2007) (multiple distinct prosecution arguments can create separate estoppels)
Southwall Techs., Inc. v. Cardinal IG Co., 54 F.3d 1570 (Fed. Cir. 1995) (prosecution arguments can create estoppel even if not strictly necessary for allowance)
Spectrum Pharm., Inc. v. Sandoz Inc., 802 F.3d 1326 (Fed. Cir. 2015) (doctrine of equivalents and prosecution history estoppel reviewed de novo)
McZeal v. Sprint Nextel Corp., 501 F.3d 1354 (Fed. Cir. 2007) (standards for Rule 12(b)(6) review in Federal Circuit practice)
Sands v. McCormick, 502 F.3d 263 (3d Cir. 2007) (Third Circuit standard for reviewing Rule 12(b)(6) dismissals)