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.

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.

Hepatoblastoma is an uncommon malignant liver cancer occurring in infants and children and composed of tissue resembling fetal liver cells, mature liver cells, or bile duct cells. They usually present with an abdominal mass. The disease is most commonly diagnosed during a child's first three years of life. Alpha-fetoprotein (AFP) levels are commonly elevated, but when AFP is not elevated at diagnosis the prognosis is poor.

Surgical removal of the tumor, adjuvant chemotherapy prior to tumor removal, and liver transplantation have been used to treat these cancers. Primary liver transplantation provides high, long term, disease-free survival rate in the range of 80%, in cases of complete tumor removal and adjuvant chemotherapy survival rates approach 100%. The presence of metastases is the strongest predictor of a poor prognosis.

Tumors that develop within the liver may be either benign (noncancerous) or malignant (cancerous). Tumors can start in the liver, or spread to the liver from another cancer in the body. Malignant liver tumors have been reported to metastasize to other organs such as regional lymph nodes, lungs, kidneys, pancreas, spleen and others.

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.

Clinical signs are often vague and include weight loss, loss of appetite, fatigue, and possible jaundice.

Fibrosarcoma occurs most frequently in the mouth in dogs . The tumor is locally invasive, and often recurs following surgery . Radiation therapy and chemotherapy are also used in treatment. Fibrosarcoma is also a rare bone tumor in dogs.

In cats, fibrosarcoma occurs on the skin. It is also the most common vaccine-associated sarcoma. In 2014, Merial launched Oncept IL-2 in Europe for the management of such feline fibrosarcomas.

There are several types of benign liver tumor.

Hemangiomas: These are the most common type of benign liver tumor, found in up to 7% of autopsy specimens. They start in blood vessels. Most of these tumors do not cause symptoms and do not need treatment. Some may bleed and need to be removed if it is mild to severe. A rare tumor is Infantile hemangioendothelioma.

Hepatic adenomas: These benign epithelial liver tumors develop in the liver and are also an uncommon occurrence, found mainly in women using estrogens as contraceptives, or in cases of steroid abuse. They are, in most cases, located in the right hepatic lobe and are frequently seen as solitary. The size of adenomas range from 1 to 30 cm. Symptoms associated with hepatic adenomas are all associate with large lesions which can cause intense abdominal pain. Over the last few decades there has been an increase with occurrences of this specific type of adenoma. The prognosis for these tumors has still not been mastered. Some correlations have been made such as malignant transformation, spontaneous hemorrhage, and rupture.

Focal nodular hyperplasia (FNH) is the second most common tumor of the liver. This tumor is the result of a congenital arteriovenous malformation hepatocyte response. This process is one in which all normal constituents of the liver are present, but the pattern by which they are presented is abnormal. Even though those conditions exist the liver still seems to perform in the normal range. Other types include nodular regenerative hyperplasia and hamartoma.

A liver metastasis is a malignant tumor in the liver that has spread from another organ affected by cancer. The liver is a common site for metastatic disease because of its rich, dual blood supply (the liver receives blood via the hepatic artery and portal vein). Metastatic tumors in the liver are 20 times more common than primary tumors. In 50% of all cases the primary tumor is of the gastrointestinal tract, other common sites include the breast, ovaries, bronchus and kidney.

Tumor emboli entering the sinusoids through the liver blood supply appear to be physically obstructed by the Kupffer cells, but if tumor emboli are larger, they tend to become lodged in the portal venous branches.

Congenital mesoblastic nephroma, while rare, is the most common kidney neoplasm diagnosed in the first three months of life and accounts for 3-5% of all childhood renal neoplasms. This neoplasm is generally non-aggressive and amenable to surgical removal. However, a readily identifiable subset of these kidney tumors has a more malignant potential and is capable of causing life-threatening metastases. Congenital mesoblastic nephroma was first named as such in 1967 but was recognized decades before this as fetal renal hamartoma or leiomyomatous renal hamartoma.

Treatment can consist of surgery (hepatectomy), chemotherapy and/or therapies specifically aimed at the liver like radiofrequency ablation, transcatheter arterial chemoembolization, selective internal radiation therapy and irreversible electroporation. For most patients no effective treatment exists because both lobes are usually involved, making surgical resection impossible. Younger patients with metastases from colorectal cancer confined to one lobe of the liver and up to 4 in number may be treated by partial hepatectomy. In selected cases, chemotherapy may be given systemically or via hepatic artery.

In some tumors, notably those arising from the colon and rectum, apparently solitary metastases

or metastases to one or other lobes may be resected. A careful search for other metastases is required, including local recurrence of the original primary tumor (e.g., via colonoscopy) and dissemination elsewhere (e.g., via CT of the thorax). 5 year survival rates of 30-40% have been reported following resection.

A cavernous liver haemangioma or hepatic haemangioma is a benign tumour of the liver composed of hepatic endothelial cells. It is the most common liver tumour, and is usually asymptomatic and diagnosed incidentally on radiological imaging. Liver haemangiomas are thought to be congenital in origin. Several subtypes exist, including the giant hepatic haemangioma, which can cause significant complications.

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.

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

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.

This large, atypical haemangioma of the liver may present with abdominal pain or fullness due to haemorrhage, thrombosis or mass effect. It may also lead to left ventricular volume overload and heart failure due to the increase in cardiac output which it causes. Further complications are Kasabach-Merritt syndrome, a form of consumptive coagulopathy due to thrombocytopaenia, and rupture.

Fibrosarcoma (fibroblastic sarcoma) is a malignant mesenchymal tumour derived from fibrous connective tissue and characterized by the presence of immature proliferating fibroblasts or undifferentiated anaplastic spindle cells in a storiform pattern. It is usually found in males aged 30 to 40 . It originates in fibrous tissues of the bone and invades long or flat bones such as femur, tibia, and mandible. It also involves periosteum and overlying muscle.

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.

Congenital mesoblastic nephroma typically (76% of cases) presents as an abdominal mass which is detected prenatally (16% of cases) by ultrasound or by clinical inspection (84% of cases) either at birth or by 3.8 years of age (median age ~1 month). The neoplasm shows a slight male preference. Concurrent findings include hypertension (19% of cases), polyhydramnios (i.e. excess of amniotic fluid in the amniotic sac) (15%), hematuria (11%), hypercalcemia (4%), and elevated serum levels of the kidney-secreted, hypertension-inducing enzyme, renin (1%). Congenital anomalies have been reported in 11 patients: 6 with genitourinary anomalies, 2 with gastrointestinal anomalies, 1 with hydrocephalus, and 1 with the Beckwith–Wiedemann syndrome. The vast majority of patients present with localized (i.e. non-metastatic) disease. Most patients' disease is classified at presentation as stage I or II (i.e. localized), few patients present with stage III (i.e. locally advanced/infiltrating), and virtually no patients present with stage IV (metastases present or V (i.e. tumors in both kidneys) disease (see staging of renal cancer).

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).

Surgery, with as wide a margin of removal as possible, has generally been the most effective and preferred way to attack LMS. If surgical margins are narrow or not clear of tumor, however, or in some situations where tumor cells were left behind, chemotherapy or radiation has been shown to give a clear survival benefit. While LMS tends to be resistant to radiation and chemotherapy, each case is different and results can vary widely.

LMS of uterine origin do frequently, but not always respond to hormonal treatments.

Dermatofibrosarcoma protuberans (DFSP)

is a very rare tumor. It is a rare neoplasm of the dermis layer of the skin, and is classified as a sarcoma. There is only about one case per million per year. DFSP is a fibrosarcoma, more precisely a cutaneous soft tissue sarcoma. In many respects, the disease behaves as a benign tumor, but in 2–5% of cases it can metastasize, so it should be considered to have malignant potential. It occurs most often in adults in their thirties; it has been described congenitally, in children, and the elderly. It accounts for approximately 2–6% of soft tissue sarcoma cancers.

Leiomyosarcoma, also referred to as LMS, is a malignant (cancerous) smooth muscle tumor. A benign tumor originating from the same tissue is termed leiomyoma. It is also important to note that while it has been believed that leiomyosarcomas do not arise from leiomyomas, there are leiomyoma variants for which classification is evolving.

About 1 person in 100,000 gets diagnosed with LMS each year. Leiomyosarcoma is one of the more common types of soft-tissue sarcoma, representing 10 percent to 20 percent of new cases. (Leiomyosarcoma of the bone is more rare.) Sarcoma is rare, consisting of only 1 percent of cancer cases in adults. Leiomyosarcomas can be very unpredictable. They can remain dormant for long periods of time and recur after years. It is a resistant cancer, meaning generally not very responsive to chemotherapy or radiation. The best outcomes occur when it can be removed surgically with wide margins early, while small and still in situ.

Mammary analogue secretory carcinoma (MASC) (also termed MASC; the "SG" subscript indicates salivary gland)) is a salivary gland neoplasm that shares a genetic mutation with certain types of breast cancer. MASC was first described by Skálová et al. in 2010. The authors of this report found a chromosome translocation in certain salivary gland tumors that was identical to the (12;15)(p13;q25) fusion gene mutation found previously in secretory carcinoma, a subtype of invasive ductal carcinoma of the breast.