Ms Gibson, a 23-year-old social media entrepreneur, convinced fans she recovered from terminal brain cancer through healthy eating and natural therapies.
Ms Ainscough, 29, recently died after trying to stave off her rare form of cancer with natural healing.
Cancer Council Victoria CEO Todd Harper is urging patients to be wary of cancer cure claims that sound too good to be true.
"We are very concerned about anyone who makes unproven scientifically flawed claims about cancer treatments because the risk is that cancer patients will take them seriously," he told AAP.
Patients should consult their doctor before trying alternative or complementary treatments, including extreme diets.
The council was concerned that if patients were "tricked by salesmen" into believing these offer alternatives to proven scientific treatments, they will either delay or avoid having them.
"We do know that nearly all of these alternative treatments are ineffective and some are actually harmful," Mr Harper said.
"It is really important that cancer patients take advantage of the (scientific proven) advances to give themselves the best opportunity for survival or at least to manage their cancer diagnosis more effectively."
Mr Harper wouldn't comment on individual cases, saying the circumstances may be complex and involve ignorance or someone being unwell.
But he said such cases did set back the Cancer Council's cause.
"Every time there is publicity about these unproven therapies, we see an increase in calls to the Cancer Council lines around the country.
"So we know that it does gather traction with people because cancer patients are very vigilant in trying to identify treatment options for themselves."
