The long-established connection between cigarette smoking and lung cancer is undisputed, but whether marijuana poses a similar threat remains under investigation.

As recreational cannabis use expands across the United States, emerging research suggests there may be cause for concern.

A recent study from Keck Medicine of USC in Southern California found that patients who have smoked marijuana heavily could face a higher risk of small cell and non-small cell lung cancer.

An earlier Keck study linked marijuana smoking with up to a fivefold higher risk of head and neck cancer compared to non-smokers.

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Brooks Udelsman, M.D., a thoracic surgeon with USC Surgery, part of Keck Medicine, said in a university report that while data points to an association, the extent of risk is still not fully known.

"If someone smokes marijuana occasionally – once a week, once a month or a few times a year – do they still have that same risk?" he asked. "My suspicion is that there is probably minimal risk."

Dr. Luis Hererra, a lung cancer and thoracic surgery specialist at Orlando Health, emphasized that there is a "clear correlation" between tobacco use and lung cancer but noted that evidence for marijuana is "less" definitive.

"However, recent studies suggest that heavier or daily smokers of cannabis have an increased risk of lung cancer," Hererra told Fox News Digital. "It is also known that marijuana smoking has some of the same chemical compounds and byproducts present in cigarettes."

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According to Hererra, smoking both marijuana and tobacco can cause direct injury to lung tissue and lead to inflammation. Over time, this kind of damage can result in cellular DNA mutations that may cause cancer.

He added that risk levels likely differ depending on how cannabis is consumed, noting that forms not involving smoke exposure appear less harmful.

Further research is required to clarify how light or intermittent cannabis smoking, as well as vaping, affects lung cancer risk, Hererra said.

He also noted that future screening guidelines may need to consider marijuana smoking as a potential risk factor.

Meanwhile, new research published in the journal *Carcinogenesis* by researchers at the University of New South Wales found that nicotine-based vaping may also elevate cancer risk.

The study’s lead author, Bernard Stewart, said their review of global research showed that "those who vape are at increased risk of cancer compared to those who don’t," adding that e-cigarettes are "likely to cause lung cancer and oral cancer."

Dr. Udelsman cautioned that vaping should not be viewed as a safer alternative to smoking, as "very severe inflammatory diseases" have begun to emerge among users.

He warned, "The data on vaping is very new, so we don’t know yet, but I’d worry about anything you’re breathing into your lungs, because it infiltrates the cells and air sacs in your lungs, which can cause damage and put you at a higher risk for cancer."

As marijuana legalization continues, both Udelsman and Hererra say the scientific community is still working to determine just how much, and under what conditions, cannabis might pose a long-term cancer risk.