Current dietary recommendations to prevent colorectal cancer include increasing the consumption of whole grains, fruits and vegetables, and reducing the intake of red meat and processed meats. Higher physical activity is also recommended. Physical exercise is associated with a modest reduction in colon but not rectal cancer risk. High levels of physical activity reduce the risk of colon cancer by about 21%. Sitting regularly for prolonged periods is associated with higher mortality from colon cancer. The risk is not negated by regular exercise, though it is lowered. The evidence for any protective effect conferred by fiber and fruits and vegetables is, however, poor. The risk of colon cancer can be reduced by maintaining a normal body weight.

It has been estimated that about half of colorectal cancer cases are due to lifestyle factors and about a quarter of all cases are preventable. Increasing surveillance, engaging in physical activity, consuming a diet high in fiber, and reducing smoking and alcohol consumption decrease the risk.

Smoking increases the risk of developing gastric cancer significantly, from 40% increased risk for current smokers to 82% increase for heavy smokers. Gastric cancers due to smoking mostly occur in the upper part of the stomach near the esophagus. Some studies show increased risk with alcohol consumption as well.

Dietary factors are not proven causes, but some foods including smoked foods, salt and salt-rich foods, red meat, processed meat, pickled vegetables, and bracken are associated with a higher risk of stomach cancer. Nitrates and nitrites in cured meats can be converted by certain bacteria, including "H. pylori", into compounds that have been found to cause stomach cancer in animals.

Fresh fruit and vegetable intake, citrus fruit intake, and antioxidant intake are associated with a lower risk of stomach cancer. A Mediterranean diet is associated with lower rates of stomach cancer, as is regular aspirin use.

Obesity is a physical risk factor that has been found to increase the risk of gastric adenocarcinoma by contributing to the development of gastroesophageal reflux disease (GERD). The exact mechanism by which obesity causes GERD is not completely known. Studies hypothesize that increased dietary fat leading to increased pressure on the stomach and the lower esophageal sphincter, due to excess adipose tissue, could play a role, yet no statistically significant data has been collected. However, the risk of gastric cardia adenocarcinoma, with GERD present, has been found to increase more than 2 times for an obese person. There is a correlation between iodine deficiency and gastric cancer.

Most tumors are adenocarcinomas, with a small percent being squamous cell carcinomas.

- Rare tumor, the U.S. incidence is 3 cases per 100,000 people each year

- Gallbladder cancer is more common in South American countries, Japan, and Israel. In Chile gallbladder cancer is the fourth most common cause of cancer deaths.

- 5th most common gastrointestinal cancer

- Up to 5 times more common in women than men depending on population (e.g. 73% female in China ).

- The age adjusted incidence rates of gall bladder cancer is highest in Chile followed by In the state of Assam in India

Smoking tobacco appears to increase the risk of breast cancer, with the greater the amount smoked and the earlier in life that smoking began, the higher the risk. In those who are long-term smokers, the risk is increased 35% to 50%. A lack of physical activity has been linked to about 10% of cases. Sitting regularly for prolonged periods is associated with higher mortality from breast cancer. The risk is not negated by regular exercise, though it is lowered.

There is an association between use of hormonal birth control and the development of premenopausal breast cancer, but whether oral contraceptives use may actually cause premenopausal breast cancer is a matter of debate. If there is indeed a link, the absolute effect is small. Additionally, it is not clear if the association exists with newer hormonal birth controls. In those with mutations in the breast cancer susceptibility genes "BRCA1" or "BRCA2", or who have a family history of breast cancer, use of modern oral contraceptives does not appear to affect the risk of breast cancer.

The association between breast feeding and breast cancer has not been clearly determined; some studies have found support for an association while others have not. In the 1980s, the abortion–breast cancer hypothesis posited that induced abortion increased the risk of developing breast cancer. This hypothesis was the subject of extensive scientific inquiry, which concluded that neither miscarriages nor abortions are associated with a heightened risk for breast cancer.

A number of dietary factors have been linked to the risk for breast cancer. Dietary factors which may increase risk include a high fat diet, high alcohol intake, and obesity-related high cholesterol levels. Dietary iodine deficiency may also play a role. Evidence for fiber is unclear. A 2015 review found that studies trying to link fiber intake with breast cancer produced mixed results. In 2016 a tentative association between low fiber intake during adolescence and breast cancer was observed.

Other risk factors include radiation and shift-work. A number of chemicals have also been linked, including polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and organic solvents Although the radiation from mammography is a low dose, it is estimated that yearly screening from 40 to 80 years of age will cause approximately 225 cases of fatal breast cancer per million women screened.

Cancer of the stomach, also called gastric cancer, is the fourth-most-common type of cancer and the second-highest cause of cancer death globally. Eastern Asia (China, Japan, Korea, Mongolia) is a high-risk area for gastric cancer, and North America, Australia, New Zealand and western and northern Africa are areas with low risk. The most common type of gastric cancer is adenocarcinoma, which causes about 750,000 deaths each year. Important factors that may contribute to the development of gastric cancer include diet, smoking and alcohol consumption, genetic aspects (including a number of heritable syndromes) and infections (for example, "Helicobacter pylori" or Epstein-Barr virus) and pernicious anemia. Chemotherapy improves survival compared to best supportive care, however the optimal regimen is unclear.

The cancer commonly spreads to the liver, bile duct, stomach, and duodenum.

Alcohol has been suggested as a risk factor for gall bladder cancer. Evidence suggests that a high intake of alcohol is associated with gall bladder cancer. Men may be at a higher risk of alcohol-related gallbladder cancer than women.

Drinking may be a cause of earlier onset of colorectal cancer. The evidence that alcohol is a cause of bowel cancer is convincing in men and probable in women.

The National Institutes of Health, the National Cancer Institute, Cancer Research, the American Cancer Society, the Mayo Clinic, and the Colorectal Cancer Coalition, American Society of Clinical Oncology and the Memorial Sloan-Kettering Cancer Center list alcohol as a risk factor.

A WCRF panel report finds the evidence "convincing" that alcoholic drinks increase the risk of colorectal cancer in men at consumption levels above 30 grams of absolute alcohol daily. The National Cancer Institute states, "Heavy alcohol use may also increase the risk of colorectal cancer"

A 2011 meta-analysis found that alcohol consumption was associated with an increased risk of colorectal cancer.

Risk factors can be divided into two categories:

- "modifiable" risk factors (things that people can change themselves, such as consumption of alcoholic beverages), and

- "fixed" risk factors (things that cannot be changed, such as age and biological sex).

The primary risk factors for breast cancer are being female and older age. Other potential risk factors include genetics, lack of childbearing or lack of breastfeeding, higher levels of certain hormones, certain dietary patterns, and obesity. Recent studies have indicated that exposure to light pollution is a risk factor for the development of breast cancer.

Factors that contribute to the development of hypopharyngeal cancer include:

- Smoking

- Chewing tobacco

- Heavy alcohol use

- Poor diet

Smoking, like lung cancer, can cause hypopharyngeal cancer because it contains carcinogens that alter the DNA or RNA in a dividing cell. These alterations may change a normal DNA sequence to an oncogene, a gene that causes cancer after exposure to a carcinogen.

Squamous cells, a type of cell that lines hollow organs like the throat, mouth, lungs, and outer layer of skin, are particularly vulnerable when exposed to cigarette smoke.

Chewing tobacco can have the same effects as smoking and is also linked to hypopharyngeal cancer. The chewing tobacco is placed into the mouth, leaving it exposed to enzymes, like amylase, which partly digests the carcinogenic material. Saliva is swallowed, along with the cancer-promoting material, which passes through the hypopharynx on its way to the esophagus.

Heavy alcohol use is linked to Hypopharyngeal Cancer as well. Alcohol damages the lining of the hypopharynx, increasing the amount of chemicals that are allowed to seep into the underlying membranes. Heavy alcohol use is also associated with nutritional deficiencies.

A disease called Plummer-Vinson syndrome, a genetic disorder that causes a long-term iron deficiency, may also lead to Hypopharyngeal Cancer. Other factors like a deficiency in certain vitamins also appear to contribute to this type of cancer.

Diet, physical inactivity and obesity are related to up to 30–35% of cancer deaths. In the United States excess body weight is associated with the development of many types of cancer and is a factor in 14–20% of cancer deaths. A UK study including data on over 5 million people showed higher body mass index to be related to at least 10 types of cancer and responsible for around 12,000 cases each year in that country. Physical inactivity is believed to contribute to cancer risk, not only through its effect on body weight but also through negative effects on the immune system and endocrine system. More than half of the effect from diet is due to overnutrition (eating too much), rather than from eating too few vegetables or other healthful foods.

Some specific foods are linked to specific cancers. A high-salt diet is linked to gastric cancer. Aflatoxin B1, a frequent food contaminant, causes liver cancer. Betel nut chewing can cause oral cancer. National differences in dietary practices may partly explain differences in cancer incidence. For example, gastric cancer is more common in Japan due to its high-salt diet while colon cancer is more common in the United States. Immigrant cancer profiles develop mirror that of their new country, often within one generation.

Worldwide approximately 18% of cancer deaths are related to infectious diseases. This proportion ranges from a high of 25% in Africa to less than 10% in the developed world. Viruses are the usual infectious agents that cause cancer but cancer bacteria and parasites may also play a role.

"Oncovirus"es (viruses that can cause cancer) include human papillomavirus (cervical cancer), Epstein–Barr virus (B-cell lymphoproliferative disease and nasopharyngeal carcinoma), Kaposi's sarcoma herpesvirus (Kaposi's sarcoma and primary effusion lymphomas), hepatitis B and hepatitis C viruses (hepatocellular carcinoma) and human T-cell leukemia virus-1 (T-cell leukemias). Bacterial infection may also increase the risk of cancer, as seen in "Helicobacter pylori"-induced gastric carcinoma. Parasitic infections associated with cancer include "Schistosoma haematobium" (squamous cell carcinoma of the bladder) and the liver flukes, "Opisthorchis viverrini" and "Clonorchis sinensis" (cholangiocarcinoma).

While some dietary factors have been associated with prostate cancer the evidence is still tentative. Evidence supports little role for dietary fruits and vegetables in prostate cancer occurrence. Red meat and processed meat also appear to have little effect in human studies. Higher meat consumption has been associated with a higher risk in some studies.

Lower blood levels of vitamin D may increase the risk of developing prostate cancer.

Folic acid supplements have no effect on the risk of developing prostate cancer.

Tobacco smoking is the main known contributor to urinary bladder cancer; in most populations, smoking is associated with over half of bladder cancer cases in men and one-third of cases among women, however these proportions have reduced over recent years since there are fewer smokers in Europe and North America. There is an almost linear relationship between smoking duration (in years), pack years and bladder cancer risk. A risk plateau at smoking about 15 cigarettes a day can be observed (meaning that those who smoke 15 cigarettes a day are approximately at the same risk as those smoking 30 cigarettes a day). Quitting smoking reduces the risk, however former smokers will most likely always be at a higher risk of bladder cancer compared to never smokers. Passive smoking has not been proven to be involved.

Thirty percent of bladder tumors probably result from occupational exposure in the workplace to carcinogens such as benzidine. 2-Naphthylamine, which is found in cigarette smoke, has also been shown to increase bladder cancer risk. Occupations at risk are bus drivers, rubber workers, motor mechanics, leather (including shoe) workers, blacksmiths, machine setters, and mechanics. Hairdressers are thought to be at risk as well because of their frequent exposure to permanent hair dyes.

In addition to these major risk factors there are also numerous other modifiable factors that are less strongly (i.e. 10–20% risk increase) associated with bladder cancer, for example, obesity. Although these could be considered as minor effects, risk reduction in the general population could still be achieved by reducing the prevalence of a number of smaller risk factor together.

It has been suggested that mutations at HRAS, KRAS2, RB1, and FGFR3 may be associated in some cases.

Pancreatic cancer is the fifth-most-common cause of cancer deaths in the United States, and the seventh most common in Europe. In 2008, globally there were 280,000 new cases of pancreatic cancer reported and 265,000 deaths. These cancers are classified as endocrine or nonendocrine tumors. The most common is ductal adenocarcinoma. The most significant risk factors for pancreatic cancer are advanced age (over 60) and smoking. Chronic pancreatitis, diabetes or other conditions may also be involved in their development. Early pancreatic cancer does not tend to result in any symptom, but when a tumor is advanced, a patient may experience severe pain in the upper abdomen, possibly radiating to the back. Another symptom might be jaundice, a yellowing of the skin and eyes.

Pancreatic cancer has a poor prognosis, with a five-year survival rate of less than 5%. By the time the cancer is diagnosed, it is usually at an advanced, inoperable stage. Only one in about fifteen to twenty patients is curative surgery attempted. Pancreatic cancer tends to be aggressive, and it resists radiotherapy and chemotherapy.

Studies suggest that drinking alcohol during pregnancy may affect the likelihood of breast cancer in daughters. "For women who are pregnant, ingestion of alcohol, even in moderation, may lead to elevated circulating oestradiol levels, either through a reduction of melatonin or some other mechanism. This may then affect the developing mammary tissue such that the lifetime risk of breast cancer is raised in their daughters."

There are also some links between prostate cancer and medications, medical procedures, and medical conditions. Use of the cholesterol-lowering drugs known as the statins may also decrease prostate cancer risk.

Infection or inflammation of the prostate (prostatitis) may increase the chance for prostate cancer while another study shows infection may help prevent prostate cancer by increasing blood flow to the area. In particular, infection with the sexually transmitted infections chlamydia, gonorrhea, or syphilis seems to increase risk. Finally, obesity and elevated blood levels of testosterone may increase the risk for prostate cancer. There is an association between vasectomy and prostate cancer; however, more research is needed to determine if this is a causative relationship.

Research released in May 2007, found that US war veterans who had been exposed to Agent Orange had a 48% increased risk of prostate cancer recurrence following surgery.

In some population studies moderate alcohol consumption is associated with increase the breast cancer risk.

In contrast, research by the Danish National Institute for Public Health, comprising 13,074 women aged 20 to 91 years, found that moderate drinking had virtually no effect on breast cancer risk.

Studies that control for screening incidence show no association with moderate drinking and breast cancer, e.g.. Moderate drinkers tend to screen more which results in more diagnoses of breast cancer, including mis-diagnoses. A recent study of 23 years of breast cancer screening in the Netherlands concluded that 50% of diagnoses were over-diagnoses.

A 2008 study commissioned by the World Health Organisation concluded that "specific fruit and vegetables may act to reduce the risk of bladder cancer." Fruit and yellow-orange vegetables, particularly carrots and those containing selenium, are probably associated with a moderately reduced risk of bladder cancer. Citrus fruits and cruciferous vegetables were also identified as having a possibly protective effect. However an analysis of 47,909 men in the Health Professionals Follow-Up Study showed little correlation between cancer reduction and high consumption of fruits and vegetables overall, or yellow or green leafy vegetables specifically, compared to the statistically significant reduction among those men who consumed large amounts of cruciferous vegetables.

In a 10-year study involving almost 49,000 men, researchers found that men who drank at least 1,44 L of water (around 6 cups) per day had a significantly reduced incidence of bladder cancer when compared with men who drank less. It was also found that: "the risk of bladder cancer decreased by 7% for every 240 mL of fluid added". The authors proposed that bladder cancer might partly be caused by the bladder directly contacting carcinogens that are excreted in urine, although this has not yet been confirmed in other studies.

Little research is conducted on these cancers due to their relative rarity when compared to the more common colorectal cancers. APC-min mice which carry a gene deficiency corresponding to that of humans with FAP also go on to develop small intestinal tumors, though humans do not.

Aflatoxin exposure can lead to the development of HCC. The aflatoxins are a group of chemicals produced by the fungi "Aspergillus flavus" (the name comes from "A. flavus" toxin) and "A. parasiticus". Food contamination by the fungi leads to ingestion of the chemicals, which are very toxic to the liver. Common foodstuffs contaminated with the toxins are cereals, peanuts and other vegetables. Contamination of food is common in Africa, South-East Asia and China. Concurrent HBV infection and aflatoxin exposure increases the risk of liver cancer to over three times that seen in HBV infected individuals without aflatoxin exposure. The mechanism by which aflatoxins cause cancer is through genetic mutation of a gene required for the prevention of cancer: p53.

Risk factors for small intestine cancer include:

- Crohn's disease

- Celiac disease

- Radiation exposure

- Hereditary gastrointestinal cancer syndromes: familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, Peutz-Jeghers syndrome

- Males are 25% more likely to develop the disease

Benign tumours and conditions that may be mistaken for cancer of the small bowel:

- Hamartoma

- Tuberculosis

In addition to virus-related cirrhosis described above, other causes of cirrhosis can lead to HCC. Alcohol intake correlates with risk of HCC, and the risk is far greater in individuals with an alcohol-induced cirrhotic liver. There are a few disorders that are known to cause cirrhosis and lead to cancer, including hereditary hemochromatosis and primary biliary cirrhosis.