From the article:
To investigate, Peng, Clapper and their colleagues examined the lungs of healthy mice and found that they contained high levels of estrogen metabolites, known as 4‑hydroxy- estrogens (4-OHEs), which are carcinogenic. Specifically, these 4-OHEs help activate processes that promote cell growth, and generate free radicals that damage cells.
When the researchers exposed the mice to tobacco smoke for 8 weeks, they found that the levels of 4-OHEs increased. “We believe that these metabolites of estrogen can damage cells and contribute to lung cancer,” says Clapper.
Female mice had twice as much 4-OHE in their lungs compared to male mice after controlling for the level of total estrogen present. Whether this is the same in humans remains to be determined. “While lung cancer is not more common in women, the number of nonsmokers who develop lung cancer is greater for men than for women,” explains Clapper.