All corrections
1
Claim
35-year-old neurosurgeon diagnosed with terminal stage 4 lung cancer.
Correction

Paul Kalanithi was 36, not 35, when he was diagnosed with stage IV lung cancer.

Full reasoning

Stanford Medicine's obituary for Paul Kalanithi states that he was diagnosed in May 2013 and that he died at age 37 on March 9, 2015. Since Kalanithi was born on April 1, 1977, a May 2013 diagnosis means he was 36 years old at diagnosis, not 35.

A separate American Lung Association review of When Breath Becomes Air says the same thing directly: Kalanithi "was 36" when he was diagnosed with stage 4 lung cancer.

So the post gets his age at diagnosis wrong by one year.

2 sources
Model: OPENAI_GPT_5 Prompt: v1.16.0