When faced with an actual or potential diagnosis of cancer, most people are inclined to consult Dr Google, often before they see a real live medical expert. Unfortunately, Dr Google doesn’t always know what’s best.

A generation ago, patients were largely dependent upon the physicians they consulted as to how best to deal with a disease like cancer. Nowadays there’s the Internet, replete with a virtual tsunami of information offered by all kinds of sources, from experts equipped with evidence-based facts to people selling products or outright quackery. The trick is to know how to tell the difference, especially since the disparate guidance provided can become a matter of life or death.

“It’s easy for people to land on a site filled with misinformation that leads them to make decisions that may not be in their best interests,” Dr Lidia Schapira, medical oncologist at Stanford University Medical Center, told me. She is editor of the very reliable site, www.cancer.net, that provides clear, scientifically-vetted information about cancer and its treatment for patients, their families and friends.

As a specialist in breast cancer, Schapira has treated women who decline postoperative therapy with a drug like tamoxifen or an aromatase inhibitor because they read on the web that the treatments are harmful, despite extensive studies showing they can help prevent a breast cancer recurrence. “The conviction about harm is an emotional reaction, and it’s very difficult for a doctor to talk facts through emotions,” she said.

As the American Cancer Society cautions, “Wrong information can hurt you when it comes to cancer. A lot of what passes for cancer information on the Internet is made up of opinion, salesmanship and testimonials and is not grounded in careful science. Anyone can post any kind of information online, and some people may be passing along information that’s limited, inaccurate or just plain wrong. Some even try to deceive you.”

Worried about an unexplained symptom? The Internet offers about two dozen “symptom checkers,” and patients can actually freak themselves out by searching the web for their symptoms and finding cancer as a possible cause. Just about any symptom, from a persistent cough to chronic constipation, can be caused by cancer, but a qualified doctor can readily rule out cancer with a proper medical examination and review of a patient’s personal and family history.

Last year in The Hartford Courant, Dr David W. Wolpaw, a family physician in Manchester, Connecticut, described a man in his 20s with a weekslong sore throat who had done an Internet search and thought he had oral cancer. The doctor reported that the man lacked risk factors for cancer, and an exam showed he had nothing worse than a cold.

“People shouldn’t expect a website to replace their physician,” Wolpaw wrote. In addition to having completed many years of education and hands-on experience, “your doctor knows you, your medical history, family history and risk factors much better than the Internet,” he added. Furthermore, he wrote, “sites can look trustworthy even when they post information not supported by scientific evidence.”

People looking for the latest iteration of snake oil will surely find it on the web. Steer clear! The cancer society cautions to beware of any postings that make claims like “scientific breakthrough”, “secret ingredient”, “miraculous cure” or “ancient remedy” as well as products offering money-back guarantees, available from only one source or said to cure a wide range of ailments.

That said, people facing cancer often can glean valuable information and support through the Internet. “The Internet can be a tool that can give people access to good scientifically-vetted information,” Schapira said. “It can help patients be better prepared for a consultation with an expert. And after such a consultation, they can check on the wisdom of the advice they got.”

She suggests relying on web-based resources that are free of commercial interests. Even sites posted by medical institutions can be self-promoting. In addition to `www.cancer.net`, which is prepared by members of the American Society of Clinical Oncology, Schapira recommended information offered by the American Cancer Society (`www.cancer.org`) and the National Cancer Institute (`www.cancer.gov`), as well as the free patient-oriented arm of a site called UpToDate that translates into lay terms the best available information that doctors get.

The cancer institute notes that the three letters attached to a site’s domain name can give people insight into the independence and validity of information it contains; best to choose .edu or .gov over .com.

Don’t be afraid to discuss alternative remedies with the doctors treating your cancer, and be sure to tell them about any such remedy you plan to try in case it can interact badly with prescribed treatments.

Nearly all major medical centres now have departments of integrative medicine, and today’s oncologists are well aware of how much the mind can influence the body’s well-being, Schapira said.