The Hirotsu decision: India tightens the screws on diagnostic patents

Summary: The Delhi High Court upheld the rejection of Hirotsu Bio Science Inc.’s patent application under Section 3(i), clarifying that “diagnosis” encompasses any process revealing a disease’s presence. By ruling that Hirotsu’s nematode screening constitutes a diagnostic step, the judgement reinforces the patent exclusion for diagnostic methods in India.

Introduction

The law on the patentability of diagnostic methods in India is very clear: they are not patentable under Section 3(i) of the Indian Patents Act, 1970. Over the last few years, the jurisprudence surrounding this exception to patentability has steadily evolved. We have previously discussed the law around Section 3(i) in these columns, here, here and here.

The latest decision in this line of cases is Hirotsu Bio Science Inc. v. Assistant Controller of Patents & Designs (Delhi High Court, C.A.(COMM.IPD-PAT) 45/2023, decision dated 17 January 2026), in which the Court affirmed the refusal of a patent application relating to a novel cancer detection technique based on nematodes’ olfactory response.

Background

The Appellant, Hirotsu Bio Science Inc., filed a national phase patent application No.  201617022947 titled: “Cancer Detection Method Using Sense of Smell of Nematode”. The application is for a cancer detection technique based on the behaviour of the nematode Caenorhabditis elegans (a type of a worm) that reportedly reacts differently to urine samples of cancer patients as compared to healthy individuals.

The main claims of the application included:

• Claim 1 is directed to an in vitro method for detecting cancer, using the nematode’s reaction to the smell of a subject-derived biological substance as an indicator.
• Claim 10 is directed to an in vitro method for identifying cancer types using modified nematodes.
• Claim 5 concerned identification of olfactory receptors in nematodes, argued to be preparatory and research-focused.

The Indian Patent Office (IPO) rejected the application primarily on grounds of Section 3(i), which statutorily bars patenting diagnostic methods. This order of the IPO was challenged by the Appellant.

Appellant’s case – Hirotsu Bio Science Inc.

The Appellant argued that the invention was merely a detection tool and not a diagnostic method. Their key contentions were:

1. ‘Detection’ vs. ‘Diagnosis’: The invention merely identified cancer-risk, without any diagnosis (which would require medical correlation, interpretation, and clinical judgment)
2. In vitro claims: Since the method was performed on biological samples outside the body, Section 3(i) should not apply.
3. Claims vs specification: Claims define monopoly, while the specification is explanatory. Thus, even if the specification described methods of diagnostics, since the claims were only limited to a detection method, the claims ought to be allowable.
4. No medical expertise or invasive step involved: Since the process does not require medical expertise or involve any invasive step, the process is not hit by Section 3(i) (EMD Millipore Corporation v. Assistant Controller of Patents and Designs, 2025:DHC:8928).
5. The process per se is not capable of identifying the disease, disorder or condition for treatment of the person, as required by Chinese University of Hong Kong and Sequenom Inc. v. The Assistant Controller of Patents and Designs 2023 SCC OnLine Mad 6372.
6. The Appellant highlighted the commercialization of the service in Japan under the brand “N-NOSE®”, where it was marketed as screening rather than diagnosis.

Respondent’s case – IPO

The IPO pushed back, arguing that the Appellant’s patent application was clearly hit by Section 3(i) for various reasons:

1. No distinction between in vivo and in vitro: Section 3(i) makes no distinction between in vivo and in vitro diagnostic methods, and excludes both from patentability.
2. All ‘essential steps’ of diagnosis performed: The invention described in the patent application carries out all the essential steps involved in diagnosis, including examination of samples, comparison with standard values, identification of deviation, and attribution of the deviation to a clinical condition.
3. End user immaterial: Section 3(i) applies regardless of whether or not the end user is a medical doctor. The fact that the method may be applied by a biomedical or veterinary practitioner to diagnose a disease/ condition does not remove it from the scope of Section 3(i).
4. Specification confirms ‘diagnosis system’: The complete specification repeatedly described the invention as a “cancer diagnosis system,” capable of detecting early-stage cancer with high accuracy.

Reliance was placed on Natera Inc. and Anr. v. Assistant Controller of Patents and Designs, 2025:DHC:8937 and Sequenom Inc. & Anr. v. Controller of Patents, 2025:DHC:8926, where it had been emphasized that diagnostic processes remain excluded even if conducted outside the body.

The decision

The Court sided with the IPO upholding the Controller’s refusal order. It focused on the following principles:

1. In vitro diagnostic processes: Section 3(i) does not contain the limiting phrase “practised on the human or animal body”, unlike the European Patent Convention. Thus, both in vivo and in vitro diagnostic methods fall within the exclusion.

2. Importance of specification: The Court held that claims cannot be read in isolation. Here, the complete specification described the method as, among other things, highly sensitive, able to detect early cancer (stage 0 or 1), useful for clinical cancer testing, and capable of diagnosing multiple cancers through a single test. The language of the specification thus makes the method inherently diagnostic.

3. Detection leading to diagnosis is also “diagnostic”: Relying on Chinese University of Hong Kong (supra) and Sequenom (supra), the Court reiterated that even screening tests qualify as diagnostic if they uncover pathology, even if further confirmation is needed. The Court rejected the argument that detection is outside Section 3(i) simply because it is not “definitive.”

4. Autonomy is immaterial: The Court clarified that whether the method is performed by doctors, technicians, or autonomously, is irrelevant. A diagnostic method remains excluded irrespective of who performs it.

Accordingly, the Court dismissed the appeal and upheld the IPO’s rejection. The Court also held that as Claim 1 itself was barred, the remaining claims, being dependent on the core Claim 1,  also failed.

Key takeaways

The Hirotsu decision is significant as it not only reinforces the judicial position that Section 3(i) of the Patents Act excludes both in vivo diagnostic methods and in vitro processes that effectively lead to diagnosis, but also clarifies that the assessment of whether the subject matter of a patent relates to a diagnostic method cannot be based on the claims alone. The specification plays an equally important role and cannot be ignored. The judgement also clarifies that the exclusion will remain even if the method is performed by a person other than a doctor.

Clearly, securing patent protection for diagnostic processes in India remains challenging. Given the jurisprudence around this issue in India presently, biotech innovators should consider claiming diagnostic innovations as devices or tools rather than processes. Drafting the patent application is also key, and must ensure that the invention is described as a detection method and not a diagnostic method.