Cancer Gene Therapy Guide: How It Works, Types, Japan Coverage

Approved treatment — bladder cancer gene therapy approved in the US (2022) and Japan (2026); nucleic acid drug imetelstat approved in the US (2024) and EU (2025) Sources: US FDA, Lancet 2024, Human Gene Therapy 2018, company releases

Cancer gene therapy delivers a therapeutic gene into a patient’s cells so that they attack the cancer or make it harder for the tumor to grow. Nadofaragene firadenovec (Adstiladrin), a gene therapy for high-risk bladder cancer that no longer responds to BCG, was approved in the US in 2022 and in Japan in May 2026, giving patients a bladder-sparing option. This guide explains how gene therapy works, the main types, results in patients and what treatment involves, based on overseas primary sources.

How does cancer gene therapy work?

The US Food and Drug Administration (FDA) describes gene therapy as a way of changing a person’s genetic material to treat disease. There are three broad approaches: replacing a disease-causing gene with a healthy copy, switching off a gene that is not working properly, or adding a new gene that helps treat the disease. In cancer care, the third approach, adding a new gene, is the most common.

A gene cannot enter a cell on its own, so it needs a carrier called a vector. The most common vector is a virus that has been stripped of its ability to cause disease. For example, an adenovirus, a type of common cold virus, can be made unable to replicate and then loaded with a therapeutic gene. Other approaches use circular DNA (plasmids) or a patient’s own immune cells, which are modified with a gene and returned to the body.

The bladder cancer drug Adstiladrin shows this principle clearly. A non-replicating adenovirus delivers the gene for the immune protein interferon alfa-2b into cells of the bladder wall. Those cells then make interferon themselves, strengthening the immune response against nearby cancer cells. Only the cells at the treatment site are changed; the therapy does not alter the reproductive cells that pass genes to children.

Gene therapy and nucleic acid drugs: the main types

Many treatments carry the word “gene”, which can be confusing. Broadly, all of them use nucleic acids such as DNA or RNA, but they work differently and have different approval status.

Sources: US FDA explanation of gene therapy and approval documents for each drug. For details see our oncolytic virus therapy guide, CAR-NK vs CAR-T and our mRNA cancer vaccine guide.

Results in patients

Bladder cancer: Adstiladrin

Adstiladrin is for high-risk non-muscle-invasive bladder cancer (cancer that has not spread into the bladder muscle) that does not respond to BCG instillation, especially when carcinoma in situ is present. In the US multicenter phase 3 study CS-003, 51% of 98 patients with carcinoma in situ achieved a complete response (no visible cancer on cystoscopy and tests). The median duration of response was 9.7 months, and 46% of complete responders stayed in response for more than a year.

In the final five-year analysis presented at the American Urological Association (AUA) meeting in 2024, 48.8% of patients were still living without bladder removal at five years, and five-year overall survival was 79.7%. In a Japanese phase 3 study of 20 patients, 75% had a complete response three months after a single instillation, as reported at the Japanese Urological Association meeting in 2025.

Myelodysplastic syndromes: imetelstat

Imetelstat (Rytelo) uses a short nucleic acid to block telomerase, an enzyme that helps cancer cells keep dividing. In the international phase 3 IMerge trial of 178 patients with lower-risk myelodysplastic syndromes who needed regular transfusions, 39.8% on imetelstat versus 15.0% on placebo went at least eight weeks without a transfusion. For at least 24 weeks the figures were 28.0% versus 3.3%, and among eight-week responders the median transfusion-free period was about one year (Lancet 2024).

Head and neck cancer: Gendicine

Gendicine, approved in China in 2003, was the world’s first cancer gene therapy. It carries the tumor-suppressor gene p53 in an adenovirus. Over 12 years it was used in more than 30,000 patients, and response rates were reported to be higher when it was combined with radiotherapy or chemotherapy than with standard treatment alone (Human Gene Therapy 2018).

Sources: US FDA approval information; Ferring releases (AUA 2024, Japanese Urological Association 2025); Platzbecker U et al., Lancet 2024; Zhang WW et al., Human Gene Therapy 2018.

What does treatment involve?

1. Checking eligibility: for bladder cancer, doctors review the course of BCG treatment and cystoscopic biopsy results; for myelodysplastic syndromes, transfusion needs and risk category.
2. Administration: Adstiladrin (75 mL) is instilled into the bladder through a urinary catheter, after a medicine to reduce bladder spasms is taken beforehand. Imetelstat is given as a two-hour intravenous infusion.
3. Repeat schedule: Adstiladrin every three months; imetelstat every four weeks.
4. Follow-up: cystoscopy and urine cytology every three months for bladder cancer, and regular blood tests for myelodysplastic syndromes, to check response and side effects.

Side effects differ by drug. With Adstiladrin, bladder symptoms such as fatigue, painful urination, urgency and blood in the urine were common, and in the five-year analysis grade 3 or higher side effects occurred in fewer than 4% of patients. With imetelstat, low white blood cell and platelet counts are common, so they are monitored with regular blood tests and managed by adjusting the dose or timing. With Gendicine, a fever lasting a few hours after injection was reported in about half of patients.

Where is it available in Japan and abroad?

• Japan: Adstiladrin was approved on May 8, 2026, added to the national health insurance price list in July, and has been used in insured care since July 15. The oncolytic virus Delytact and CAR-T therapies are also approved in Japan.
• United States: Adstiladrin (December 2022) and imetelstat (June 2024) are approved and prescribed.
• Europe: imetelstat received European Union approval in March 2025.
• China: Gendicine has been in use since 2003.

For another bladder-sparing option in BCG-unresponsive bladder cancer, see BCG-unresponsive bladder cancer: Anktiva. Our overview of nucleic acid medicine in Japan is at Nucleic acid medicine & aptamers.

Questions to ask your doctor

• Is there an approved gene therapy or nucleic acid drug for my type and stage of cancer?
• If my bladder cancer did not respond to BCG, which tests decide whether a bladder-sparing gene therapy suits me?
• When, and with which tests, will we check whether the treatment is working?
• Which symptoms mean I should contact the hospital straight away?

FAQ

Does cancer gene therapy permanently change my genes?

Approved cancer gene therapies are designed to work in cells at the treatment site or in immune cells, and they do not change the reproductive cells that pass genes to children. Adstiladrin works by having bladder-wall cells make interferon to strengthen the immune response.

Is gene therapy the same as genetic testing?

No. Genetic testing looks for changes in cancer cells to help choose the right drug, while gene therapy puts a therapeutic gene into the body to treat the disease directly.

Is bladder cancer gene therapy covered by insurance in Japan?

Adstiladrin was approved in Japan in May 2026 and added to the national health insurance price list in July, so it is used in insured care. Your urologist decides whether you fit the approved use, such as BCG-unresponsive high-risk non-muscle-invasive bladder cancer.

Are the side effects of cancer gene therapy severe?

It depends on the drug. Adstiladrin, given into the bladder, mostly caused mild bladder symptoms, with grade 3 or higher effects in fewer than 4% of patients. Imetelstat often lowers blood counts, which are monitored with blood tests and managed by adjusting the dose.

Sources

• US FDA — FDA approves first adenoviral vector-based gene therapy for high-risk, BCG-unresponsive non-muscle invasive bladder cancer (nadofaragene firadenovec-vncg, 2022-12-16)
  fda.gov
  Checked: 2026-10-27
• US FDA — What is gene therapy?
  fda.gov
  Checked: 2026-10-27
• Ferring — Final five-year analysis of phase 3 data with ADSTILADRIN shows durable bladder preservation and consistent long-term safety in BCG-unresponsive NMIBC (AUA 2024)
  businesswire.com
  Checked: 2026-10-27
• Ferring Japan — PMDA acceptance of NDA filing for nadofaragene firadenovec (Japanese phase 3 initial results, 2025-09)
  businesswire.com
  Checked: 2026-10-27
• PHARMA JAPAN — Ferring nabs Japan approval for bladder cancer gene therapy (2026-05-12)
  pj.jiho.jp
  Checked: 2026-10-27
• PHARMA JAPAN — Ferring’s Adstiladrin, Boehringer’s Jascayd hit market (2026-07-16)
  pj.jiho.jp
  Checked: 2026-10-27
• Geron — FDA approval of RYTELO (imetelstat), a first-in-class telomerase inhibitor, for lower-risk MDS with transfusion-dependent anemia (2024-06)
  businesswire.com
  Checked: 2026-10-27
• Platzbecker U et al. Imetelstat in patients with lower-risk myelodysplastic syndromes (IMerge): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet 2024;403:249–260
  doi.org/10.1016/S0140-6736(23)01724-5
  Checked: 2026-10-27
• CURE — EU approves Rytelo for transfusion-dependent anemia in lower-risk MDS (2025-03)
  curetoday.com
  Checked: 2026-10-27
• Zhang WW et al. The first approved gene therapy product for cancer Ad-p53 (Gendicine): 12 years in the clinic. Human Gene Therapy 2018;29(2)
  doi.org/10.1089/hum.2017.218
  Checked: 2026-10-27

Written by the FTH editorial team. Sources checked 2026-10-27 · Medical review: not applicable

This article is general information based on public sources and does not replace diagnosis or treatment. Please discuss treatment decisions with your medical team.