You first say that 1) NAC, 2) "causes cancer", 3) "in humans".
You then back that up with a study doesn't provide evidence for all three claims. The study is about mice that are genetically altered to develop lung tumors after virus inhalation. The study doesn't indicate that cancer is caused, but that tumors develop faster. The study is not about NAC, but about supplementation of both NAC and Vitamin E.
The study is also unclear about how much NAC and Vitamin E the mice were fed through water and chow, but they seem to have been fed quite large dose. If I do some napkin calculations based on average eating, drinking and mouse weight, it would be 133 mg of NAC per kg of body weight. While a normal dose of NAC for a human would be 600 to 1800 mg per day, which for a 65 kg human comes down to 28 mg per kg of body weight.
It's a relevant study, but a far cry from your initial statement. Your initial statement was also very short, low-effort and required clarification from someone else.
You probably also would argue smoking cigarettes doesn’t cause cancer? Where there’s smoke, there’s fire.
Edit: to connect the dots:
How mice studies are used
Experiments on mice have helped scientists understand how the carcinogens in cigarette smoke damage DNA and cause cancer, which complements epidemiological data from human studies.
These animal studies have been crucial in establishing the link between smoking and cancer since at least the 1950s.
No, I merely called you out on the enormous discrepancy between your first (false, unproven) statement and your second statement, and did some work clarifying the details where you only made lazy statements.
You could have said that there's limited evidence from a single mouse study that suggests that NAC might promote tumor growth in humans as well. That's fair. But you didn't. You (falsely) stated that "NAC causes cancer in humans".
There’s more but that’s just one example.