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Cancer

FDA Updates Indication for Bluebird Bio's Skysona Gene Therapy Amid Cancer Concerns

Strategic Insights

— 2 min read

The FDA has recently updated the indication for Skysona, a gene therapy developed by bluebird bio, to restrict its use in patients who do not have an available human leukocyte antigen (HLA)-matched donor for stem cell transplant. This decision comes after the agency expressed concerns about an increased risk of blood cancer associated with the treatment. Skysona is approved to treat cerebral adrenoleukodystrophy (CALD), a rare inherited neurological disorder. The FDA has added a boxed warning to the drug's label, highlighting the risk of hematologic malignancies, including myelodysplastic syndrome and acute myeloid leukemia, which are linked to the insertion of Skysona's lentiviral vector into the human genome. Despite the risks, some patients have benefited from the treatment, but the FDA advises lifelong monitoring for blood cancer, including regular blood tests and assessments.

Key Takeaways:

  • The FDA has updated the indication for Skysona to restrict its use in patients without an HLA-matched donor for stem cell transplant due to concerns about blood cancer risk.
  • Skysona is approved to treat cerebral adrenoleukodystrophy (CALD), a rare inherited neurological disorder, but carries a risk of hematologic malignancies, including myelodysplastic syndrome and acute myeloid leukemia.
  • As of July 2025, hematologic malignancies have been diagnosed in 10 (15%) of 67 clinical trial participants, compared with three (4%) incidents at the time of Skysona's initial approval in 2022.
  • The FDA has added a boxed warning to the drug's label, advising patients to undergo regular blood tests and assessments for evidence of clonal expansion or predominance annually after the first year of treatment.
  • No sales of Skysona were reported in the first three months of 2025, with a list price of $3 million per treatment.
  • Other gene therapies, such as Zynteglo and Lyfgenia, have seen sales of $26.3 million and $12.4 million, respectively, during the same period.
  • Bluebird bio has sold the company to Carlyle and SK Capital Partners for $49 million, including an alternative payment method tied to the company's future revenue performance.

Statistics:

  • 10 out of 67 clinical trial participants (15%) developed hematologic malignancies as of July 2025.
  • 3 out of 67 clinical trial participants (4%) developed hematologic malignancies at the time of Skysona's initial approval in 2022.
  • 67 clinical trial participants received Skysona treatment, resulting in 10 cases of hematologic malignancies.
  • The FDA advises patients to undergo complete blood count checks at least every three months and thorough assessments for evidence of clonal expansion or predominance annually after the first year of treatment.
  • Skysona's list price is $3 million per treatment, with no sales reported in the first three months of 2025.
  • Zynteglo and Lyfgenia generated sales of $26.3 million and $12.4 million, respectively, during the first quarter of 2025.

Sources:

  • [Source 1] FDA approval of Skysona in 2022
  • [Source 2] Bluebird bio's quarterly report filed in May 2025
  • [Source 3] FDA update on Skysona's indication in November 2024
  • [Source 4] Carlyle and SK Capital Partners acquisition of bluebird bio in July 2025

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