HCC mostly occurs in people with cirrhosis of the liver, and so risk factors generally include factors which cause chronic liver disease that may lead to cirrhosis. Still, certain risk factors are much more highly associated with HCC than others. For example, while heavy alcohol consumption is estimated to cause 60-70% of cirrhosis, the vast majority of HCC occurs in cirrhosis attributed to viral hepatitis (although there may be overlap). Recognized risk factors include:

- Chronic viral hepatitis (estimated cause of 80% cases globally)

- Chronic hepatitis B (approximately 50% cases)

- Chronic hepatitis C (approximately 25% cases)

- Toxins:

- Alcohol abuse: the most common cause of cirrhosis

- Aflatoxin

- Iron overload state (Hemochromatosis)

- Metabolic:

- Nonalcoholic steatohepatitis: up to 20% progress to cirrhosis

- Type 2 diabetes (probably aided by obesity)

- Congenital disorders:

- Alpha 1-antitrypsin deficiency

- Wilson's disease (controversial; while some theorise the risk increases, case studies are rare and suggest the opposite where Wilson's disease actually may confer protection)

- Hemophilia, although statistically associated with higher risk of HCC, this is due to coincident chronic viral hepatitis infection related to repeated blood transfusions over lifetime.

The significance of these risk factors varies globally. In regions where hepatitis B infection is endemic, such as southeast China, this is the predominant cause. In populations largely protected by hepatitis B vaccination, such as the United States, HCC is most often linked to causes of cirrhosis such as chronic hepatitis C, obesity, and alcohol abuse.

Certain benign liver tumors, such as hepatocellular adenoma, may sometimes be associated with coexisting malignant HCC. There is limited evidence for the true incidence of malignancy associated with benign adenomas; however, the size of hepatic adenoma is considered to correspond to risk of malignancy and so larger tumors may be surgically removed. Certain subtypes of adenoma, particularly those with β-catenin activation mutation, are particularly associated with increased risk of HCC.

Children and adolescents are unlikely to have chronic liver disease, however, if they suffer from congenital liver disorders, this fact increases the chance of developing hepatocellular carcinoma. Specifically, children with biliary atresia, infantile cholestasis, glycogen-storage diseases, and other cirrhotic diseases of the liver are predisposed to developing HCC in childhood.

Young adults afflicted by the rare fibrolamellar variant of hepatocellular carcinoma may have none of the typical risk factors, i.e. cirrhosis and hepatitis.

The risk of hepatocellular carcinoma in type 2 diabetics is greater (from 2.5 to 7.1 times the non diabetic risk) depending on the duration of diabetes and treatment protocol. A suspected contributor to this increased risk is circulating insulin concentration such that diabetics with poor insulin control or on treatments that elevate their insulin output (both states that contribute to a higher circulating insulin concentration) show far greater risk of hepatocellular carcinoma than diabetics on treatments that reduce circulating insulin concentration. On this note, some diabetics who engage in tight insulin control (by keeping it from being elevated) show risk levels low enough to be indistinguishable from the general population. This phenomenon is thus not isolated to diabetes mellitus type 2 since poor insulin regulation is also found in other conditions such as metabolic syndrome (specifically, when evidence of non alcoholic fatty liver disease or NAFLD is present) and again there is evidence of greater risk here too. While there are claims that anabolic steroid abusers are at greater risk (theorized to be due to insulin and IGF exacerbation), the only evidence that has been confirmed is that anabolic steroid users are more likely to have hepatocellular adenomas (a benign form of HCC) transform into the more dangerous hepatocellular carcinoma.

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.

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.

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.

Alcohol is a risk factor for liver cancer, through cirrhosis. "Cirrhosis results from scar formation within the liver, most commonly due to chronic alcohol use."

"Approximately 5 percent of people with cirrhosis develop liver cancer. Cirrhosis is a disease that develops when liver cells are replaced with scar tissue after damage from alcohol abuse, …"

The NIAAA reports that "Prolonged, heavy drinking has been associated in many cases with primary liver cancer." However, it is liver cirrhosis, whether caused by alcohol or another factor, that is thought to induce the cancer."

"The chances of getting liver cancer increase markedly with five or more drinks per day" (NCI).

A study concluded that for every additional drink regularly consumed per day, the incidence of liver cancer increases by 0.7 per 1000.

In the United States, liver cancer is relatively uncommon, afflicting approximately 2 people per 100,000, but excessive alcohol consumption is linked to as many as 36% of these cases by some investigators "Overall, 61% of HCC were attributable to HCV [hepatitis C virus], 13% to HBV [hepatitis B virus], and 18% to heavy alcohol drinking." A study in the province of Brescia, northern Italy concluded, "On the basis of population attributable risks (AR), heavy alcohol intake seems to be the single most relevant cause of HCC in this area (AR: 45%), followed by HCV (AR: 36%), and HBV (AR: 22%) infection."

FHCC accounts for 1-10% of primary liver cancers. It typically has a young age at presentation (20–40 years: mean age ~27 years) when compared to conventional HCC. Unlike the more common HCC, patients most often do not have coexistent liver disease such as cirrhosis.

Fibrolamellar hepatocellular carcinoma (FHCC) is a rare form of hepatocellular carcinoma (HCC) that typically affects young adults and is characterized, under the microscope, by laminated fibrous layers interspersed between the tumour cells. Approximately 200 new cases are diagnosed worldwide each year.

Malignant neoplasm of liver and intrahepatic bile ducts. The most frequent forms are metastatic malignant neoplasm of liver)

- liver cell carcinoma

- hepatocellular carcinoma

- hepatoma

- cholangiocarcinoma

- hepatoblastoma

- angiosarcoma of liver

- Kupffer cell sarcoma

- other sarcomas of liver

Benign neoplasm of liver include hepatic hemangiomas, hepatic adenomas, and focal nodular hyperplasia (FNH).

These differ according to the type of chronic liver disease.

- Excessive alcohol use

- Obesity

- Metabolic syndrome including raised blood lipids

- Health care professionals who are exposed to body fluids and infected blood

- Sharing infected needle and syringes

- Having unprotected sex and multiple sex partners

- Working with toxic chemicals without wearing safety clothes

- Certain prescription medications

Liver tumors or hepatic tumors are tumors or growths on or in the liver (medical terms pertaining to the liver often start in "hepato-" or "hepatic" from the Greek word for liver, "hepar"). Several distinct types of tumors can develop in the liver because the liver is made up of various cell types. These growths can be benign or malignant (cancerous). They may be discovered on medical imaging (even for a different reason than the cancer itself), or may be present in patients as an abdominal mass, hepatomegaly, abdominal pain, jaundice, or some other liver dysfunction.

Chronic liver diseases like chronic hepatitis, chronic alcohol abuse or chronic toxic liver disease may cause

- liver failure and hepatorenal syndrome

- fibrosis and cirrhosis of liver

Cirrhosis may also occur in primary biliary cirrhosis. Rarely, cirrhosis is congenital.

Hepatoid tumor or hepatoid [adeno]carcinoma are terms for a number of uncommon or rare neoplasms in humans, named for a visual resemblance of the cells under the microscope to those of hepatocellular carcinoma, the most common form of liver cancer. They can arise in several parts of the body, and thus form sub-types of diseases such as stomach cancer and pancreatic cancer. The WHO defines "Hepatoid carcinoma" as "An adenocarcinoma with morphologic characteristics similar to hepatocellular carcinoma , arising from an anatomic site other than the liver".

In dogs it may refer to a Perianal gland tumor, based on a similar resemblance to healthy liver cells.

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.

Prognosis and treatment is the same as for the most common type of ovarian cancer, which is epithelial ovarian cancer.

The median survival of primary peritoneal carcinomas is usually shorter by 2–6 months time when compared with serous ovarian cancer. Studies show median survival varies between 11.3–17.8 months. One study reported 19-40 month median survival (95% CI) with a 5-year survival of 26.5%.

Elevated albumin levels have been associated with a more favorable prognosis.

As of 2009, there have been approximately 120 reported cases of renal medullary carcinoma. In every instance except for one, the patients were positive for cell sickling. Wilms' tumor, the most common renal tumor of childhood, is responsible for 6-7% of childhood cancer whereas all remaining primary renal tumors (among which is included renal medullary carcinoma) collectively account for less than 1% of all childhood cancer and less than 10% of primary kidney tumors in childhood.

Key prevention strategies for cirrhosis are population-wide interventions to reduce alcohol intake (through pricing strategies, public health campaigns, and personal counseling), programs to reduce the transmission of viral hepatitis, and screening of relatives of people with hereditary liver diseases.

Little is known about factors affecting cirrhosis risk and progression. Research has suggested that coffee consumption appears to help protect against cirrhosis.

In most series, LCLC's comprise between 5% and 10% of all lung cancers.

According to the Nurses' Health Study, the risk of large cell lung carcinoma increases with a previous history of tobacco smoking, with a previous smoking duration of 30 to 40 years giving a relative risk of approximately 2.3 compared to never-smokers, and a duration of more than 40 years giving a relative risk of approximately 3.6.

Another study concluded that cigarette smoking is the predominant cause of large cell lung cancer. It estimated that the odds ratio associated with smoking two or more packs/day for current smokers is 37.0 in men and 72.9 in women.

Hepatocellular carcinoma is a primary liver cancer that is more common in people with cirrhosis. People with known cirrhosis are often screened intermittently for early signs of this tumor, and screening has been shown to improve outcomes.

When associated with the lung, it is typically a centrally located large cell cancer (non-small cell lung cancer or NSCLC). It often has a paraneoplastic syndrome causing ectopic production of parathyroid hormone-related protein (PTHrP), resulting in hypercalcemia, however paraneoplastic syndrome is more commonly associated with small cell lung cancer.

It is primarily due to smoking.

Adult survivors of childhood cancer have some physical, psychological, and social difficulties.

Premature heart disease is a major long-term complication in adult survivors of childhood cancer. Adult survivors are eight times more likely to die of heart disease than other people, and more than half of children treated for cancer develop some type of cardiac abnormality, although this may be asymptomatic or too mild to qualify for a clinical diagnosis of heart disease.

Since the cancer most often presents at an advanced stage, prognosis is generally very poor, with median survival times of 3 months (range 1–7 months). Longer survival of beyond one year was reported in one patient and of up to eight years in one individual whose tumor was well circumscribed and non-metastatic at the time of diagnosis, suggesting that early detection could dramatically improve survival.

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).

Human papillomavirus infection (HPV) has been associated with SCC of the oropharynx, lung, fingers and anogenital region.

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.