In male dogs, the tumor affects the penis and foreskin. In female dogs, it affects the vulva. Rarely, the mouth or nose are affected. The tumor often has a cauliflower-like appearance. Signs of genital TVT include a discharge from the prepuce and in some cases urinary retention, from blockage of the urethra. Signs of a nasal TVT include nasal fistulae, nosebleeds and other nasal discharge, facial swelling, and enlargement of the submandibular lymph nodes.

Canine transmissible venereal tumors (CTVTs), also called transmissible venereal tumors (TVTs), canine transmissible venereal sarcoma (CTVS), sticker tumors and infectious sarcoma is a histiocytic tumor of the external genitalia of the dog and other canines, and is transmitted from animal to animal during mating. It is one of only three known transmissible cancers in mammals; other are devil facial tumor disease, a cancer which occurs in Tasmanian devils, and contagious reticulum cell sarcoma of the Syrian hamster.

The tumor cells are themselves the infectious agents, and the tumors that form are not genetically related to the host dog. Although the genome of a CTVT is derived from a canid (probably a dog, wolf or coyote), it is now essentially living as a unicellular, asexually reproducing (but sexually transmitted) pathogen. Sequence analysis of the genome suggests it diverged from canids over 6,000 years ago; possibly much earlier. The most recent estimates of its time of origin place date it to about 11,000 years ago. However, the most recent common ancestor of "extant" tumors is more recent: it probably originated 200 to 2,500 years ago.

Canine TVTs were initially described by Russian veterinarian M.A. Novinsky (1841–1914) in 1876, when he demonstrated that the tumor could be transplanted from one dog to another by infecting them with tumor cells.

Symptoms of cancer in dogs may include:

- Lumps (which are not always malignant, but should always be examined by a vet)

- Swelling

- Persistent sores

- Abnormal discharge from any part of the body

- Bad breath

- Listlessness/lethargy

- Rapid, often unexplained weight loss

- Sudden lameness

- Offensive odor

- Black, tarry stools (a symptom of ulcers, which can be caused by mast cell tumors)

- Decreased or loss of appetite

- Difficulty breathing, urinating or defecating

A transmissible cancer is a cancer cell or cluster of cancer cells that can be transferred between individuals without the involvement of an infectious agent, such as an oncovirus. Transmission of cancer between humans is rare.

Contagious cancers occur in dogs, Tasmanian devils, Syrian hamsters, and some marine bivalves including soft-shell clams. These cancers have a relatively stable genome as they are transmitted.

In humans, a significant fraction of Kaposi's sarcoma occurring after transplantation may be due to tumorous outgrowth of donor cells. Although Kaposi's sarcoma is caused by a virus (Kaposi's sarcoma-associated herpesvirus), in these cases, it appears likely that transmission of virus-infected tumor cells—rather than the free virus—caused tumors in the transplant recipients.

DFTD tumours are "large, solid, soft tissue masses usually with flattened, centrally ulcerated, and surfaces", which are "typically multicentric, appearing first in the oral, face, or neck regions", and are " to nodular aggregates of round to spindle-shaped cells, often within a pseudocapsule and divided into lobules by delicate fibrous septae". The disease is described as being aggressive, locally. Tumours can cover the eyes.

As Iain O'Neill notes, it also presents a "high rate of regional lymph node involvement and systemic metastasis"; of the avenues by which the cancer can spread systemically, metastasis to the lungs, spleen, and heart are observed, as is secondary "intracranial involvement". O'Neill also notes that "organ involvement and superimposed infection may... contribute to mortality." Moreover, growth of large tumours impedes feeding, and starvation is another cause of death in affected devils.

These tumors are usually benign, but can become malignant over time. They vary in size, and can be found as singles or multiples. They are most commonly found in mature grey horses (less than 15 years old) and are typically found under the tail, around the anus, and on the external genitalia.

Cancer is the leading cause of death in dogs. It is estimated that 1 in 3 domestic dogs will develop cancer, which is the same incidence of cancer among men. Dogs can develop a variety of cancers and most are very similar to those found in humans. Dogs can develop carcinomas of epithelial cells and organs, sarcomas of connective tissues and bones, and lymphomas or leukemias of the circulatory system. Selective breeding of dogs has led certain pure-bred breeds to be at high-risk for specific kinds of cancer.

Veterinary oncology is the medical study of cancer in animals, and can be diagnosed and treated by specialized veterinarians called veterinary oncologists.

These tumors are frequently malignant and have a high tendency to spread to other organs. They are most commonly found in grey horses who are over the age of 15 and are found as a large coalescing mass under the tail, around the anus, on the external genitalia, or the parotid salivary gland.

When mastocytomas affect humans, they are typically found in skin. They usually occur as a single lesion on the trunk or wrist. Although it is rare, mastocytomas are sometimes found in the lung. It can also affect children.

Mast cell tumors are known among veterinary oncologists as 'the great pretenders' because their appearance can be varied, from a wart-like nodule to a soft subcutaneous lump (similar on palpation to a benign lipoma) to an ulcerated skin mass. Most mast cell tumors are small, raised lumps on the skin. They may be hairless, ulcerated, or itchy. They are usually solitary, but in about six percent of cases, there are multiple mast cell tumors (especially in Boxers and Pugs).

Manipulation of the tumor may result in redness and swelling from release of mast cell granules, also known as Darier's sign, and prolonged local hemorrhage. In rare cases, a highly malignant tumor is present, and signs may include loss of appetite, vomiting, diarrhea, and anemia. The presence of these signs usually indicates mastocytosis, which is the spread of mast cells throughout the body. Release of a large amount of histamine at one time can result in ulceration of the stomach and duodenum (present in up to 25 percent of cases) or disseminated intravascular coagulation. When metastasis does occur, it is usually to the liver, spleen, lymph nodes and bone marrow.

Commonly affected areas include the lower limbs, back, face, mouth, and genitalia. The lesions are usually as described above, but may occasionally be plaque-like (often on the soles of the feet) or even involved in skin breakdown with resulting fungating lesions.

Associated swelling may be from either local inflammation or lymphoedema (obstruction of local lymphatic vessels by the lesion). Skin lesions may be quite disfiguring for the sufferer, and a cause of much psychosocial pathology.

KS lesions are nodules or blotches that may be red, purple, brown, or black, and are usually papular.

They are typically found on the skin, but spread elsewhere is common, especially the mouth, gastrointestinal tract and respiratory tract. Growth can range from very slow to explosively fast, and is associated with significant mortality and morbidity.

Devil facial tumour disease (DFTD) is an aggressive non-viral clonally transmissible cancer which affects Tasmanian devils, a marsupial native to Australia.

DFTD was first described in 1996. In the subsequent decade the disease ravaged Tasmania's wild devils, with estimates of decline ranging from 20% to as much as 50% of the devil population, across over 65% of the state. Affected high-density populations suffer up to 100% mortality in 12–18 months. The disease has mainly been concentrated in Tasmania's eastern half. Visible signs of DFTD begin with lesions and lumps around the mouth. These develop into cancerous tumours that may spread from the face to the entire body. Devils usually die within six months from organ failure, secondary infection, or metabolic starvation as the tumours interfere with feeding. As of 2010, 80% of population is infected, and only 0.1% is not affected. DFTD affects males and females equally. As of 2010, the population had been reduced by 70% (from 1996 census data), and if a cure is not found, a prediction has been made that the species will become extinct by 2035.

The most plausible route of transmission is through biting, particularly when canine teeth come into direct contact with the diseased cells. Other modes of transmission that cannot be discounted, yet haven't been conclusively proven, are the ingesting of an infected carcass and the sharing of food, both of which involve an allogeneic transfer of cells between unrelated individuals.. The cancer seems to infect the fittest devil individuals, which are socially dominant. Animals that eventually become infected survive at a higher rate and reproduce more before dying of the disease than devils that don’t get the cancer.

As of 2010, six females had been reported to have been found with partial immunity to DTF, and breeding in captivity was begun in an attempt to save the population.

The exact causes for the development of canine mammary tumors are not fully understood. However, hormones of the estrous cycle seem to be involved. Female dogs who are not spayed or who are spayed later than the first heat cycle are more likely to develop mammary tumors. Dogs have an overall reported incidence of mammary tumors of 3.4 percent. Dogs spayed before their first heat have 0.5 percent of this risk, and dogs spayed after just one heat cycle have 8 percent of this risk. The tumors are often multiple. The average age of dogs with mammary tumors is ten to eleven years old. Obesity at one year of age and eating red meat have also been associated with an increased risk for these tumors, as has the feeding of high fat homemade diets.

There are several hypotheses on the molecular mechanisms involved in the development of canine mammary tumors but a specific genetic mutation has not been identified.

A mammary tumor is a neoplasm originating in the mammary gland. It is a common finding in older female dogs and cats that are not spayed, but they are found in other animals as well. The mammary glands in dogs and cats are associated with their nipples and extend from the underside of the chest to the groin on both sides of the midline. There are many differences between mammary tumors in animals and breast cancer in humans, including tumor type, malignancy, and treatment options. The prevalence in dogs is about three times that of women. In dogs, mammary tumors are the second most common tumor (after skin tumors) over all and the most common tumor in female dogs with a reported incidence of 3.4%. Multiple studies have documented that spaying female dogs when young greatly decreases their risk of developing mammary neoplasia when aged. Compared with female dogs left intact, those spayed before puberty have 0.5% of the risk, those spayed after one estrous cycle have 8.0% of the risk, and dogs spayed after two estrous cycles have 26.0% of the risk of developing mammary neoplasia later in life. Overall, unspayed female dogs have a seven times greater risk of developing mammary neoplasia than do those that are spayed. While the benefit of spaying decreases with each estrous cycle, some benefit has been demonstrated in female dogs even up to 9 years of age. There is a much lower risk (about 1 percent) in male dogs and a risk in cats about half that of dogs.

Animals that have undergone population bottlenecks may be at greater risks of contracting transmissible cancers. Because of their transmission, it was initially thought that these diseases were caused by the transfer of oncoviruses, in the manner of cervical cancer caused by HPV.

- Canine transmissible venereal tumor (CTVT) is sexually transmitted cancer in dogs. It was experimentally transplanted between dogs in 1876 by M. A. Novinsky (1841–1914). A single malignant clone of CTVT cells has colonized dogs worldwide, representing the oldest known malignant cell line in continuous propagation.

- Contagious reticulum cell sarcoma of the Syrian hamster can be transmitted from one Syrian hamster to another by means of the bite of the mosquito "Aedes aegypti".

- Devil facial tumour disease (DFTD) is a transmissible parasitic cancer in the Tasmanian devil.

- Soft-shell clams, "Mya arenaria", have been found to be vulnerable to a transmissible neoplasm of the hemolymphatic system — effectively, leukemia.

- Horizontally transmitted cancers have also been discovered in three other species of marine bivalves: bay mussels ("Mytilus trossulus"), common cockles ("Cerastoderma edule") and golden carpet shell clams ("Polititapes aureus"). The golden carpet shell clam cancer was found to have been transmitted from another species, the pullet carpet shell ("Venerupis corrugata").

General signs and symptoms include depression, fever, weight loss, loss of appetite, loss of hair or fur and vomiting. Lymphoma is the most common cancerous cause of hypercalcemia (high blood calcium levels) in dogs. It can lead to the above signs and symptoms plus increased water drinking, increased urination, and cardiac arrhythmias. Hypercalcemia in these cases is caused by secretion of parathyroid hormone-related protein.

Multicentric lymphoma presents as painless enlargement of the peripheral lymph nodes. This is seen in areas such as under the jaw, the armpits, the groin, and behind the knees. Enlargement of the liver and spleen causes the abdomen to distend. Mediastinal lymphoma can cause fluid to collect around the lungs, leading to coughing and difficulty breathing. Hypercalcemia is most commonly associated with this type.

Gastrointestinal lymphoma causes vomiting, diarrhea, and melena (digested blood in the stool). Low serum albumin levels and hypercalcemia can also occur.

Lymphoma of the skin is an uncommon occurrence. The epitheliotropic form typically appears as itchy inflammation of the skin progressing to nodules and plaques.

The non-epitheliotropic form can have a wide variety of appearances, from a single lump to large areas of bruised, ulcerated, hairless skin. The epitheliotropic form must be differentiated from similar appearing conditions such as pemphigus vulgaris, bullous pemphigoid, and lupus erythematosus.

Signs for lymphoma in other sites depend on the location. Central nervous system involvement can cause seizures or paralysis. Eye involvement, seen in 20 to 25 percent of cases, can lead to glaucoma, uveitis, bleeding within the eye, retinal detachment, and blindness. Lymphoma in the bone marrow causes anemia, low platelet count, and low white blood cell count.

When cancer begins, it produces no symptoms. Signs and symptoms appear as the mass grows or ulcerates. The findings that result depend on the cancer's type and location. Few symptoms are specific. Many frequently occur in individuals who have other conditions. Cancer is a "great imitator". Thus, it is common for people diagnosed with cancer to have been treated for other diseases, which were hypothesized to be causing their symptoms.

People may become anxious or depressed post-diagnosis. The risk of suicide in people with cancer is approximately double.

The cancer is classified into low and high grade types. Classification is also based on location. The four location types are multicentric, mediastinal, gastrointestinal, and extranodal (involving the kidney, central nervous system, skin, heart, or eye). Multicentric lymphoma, the most common type (by greater than 80 percent), is found in the lymph nodes, with or without involvement in the liver, spleen, or bone marrow. Mediastinal lymphoma occurs in the lymph nodes in the thorax and possibly the thymus. Gastrointestinal lymphoma occurs as either a solitary tumor or diffuse invasion of the stomach or intestines, with or without involvement in the surrounding lymph nodes, liver or spleen. Classification is further based on involvement of B-lymphocytes or T-lymphocytes. Approximately 70 percent are B-cell lymphoma. Cutaneous lymphoma can be classified as epitheliotropic (closely conforming to the epidermis) or non-epitheliotropic. The epitheliotropic form is typically of T-cell origin and is also called mycosis fungoides. The non-epitheliotropic form is typically of B-cell origin.

Local symptoms may occur due to the mass of the tumor or its ulceration. For example, mass effects from lung cancer can block the bronchus resulting in cough or pneumonia; esophageal cancer can cause narrowing of the esophagus, making it difficult or painful to swallow; and colorectal cancer may lead to narrowing or blockages in the bowel, affecting bowel habits. Masses in breasts or testicles may produce observable lumps. Ulceration can cause bleeding that, if it occurs in the lung, will lead to coughing up blood, in the bowels to anemia or rectal bleeding, in the bladder to blood in the urine and in the uterus to vaginal bleeding. Although localized pain may occur in advanced cancer, the initial swelling is usually painless. Some cancers can cause a buildup of fluid within the chest or abdomen.

Two thirds of cases are located in the anterior maxilla, and one third are present in the anterior mandible.

Two thirds of the cases are associated with an impacted tooth (usually being the canine).

On radiographs, the adenomatoid odontogenic tumor presents as a radiolucency (dark area) around an unerupted tooth extending past the cementoenamel junction.

It should be differentially diagnosed from a dentigerous cyst and the main difference is that the radiolucency in case of AOT extends apically beyond the cementoenamel junction.

Radiographs will exhibit faint flecks of radiopacities surrounded by a radiolucent zone.

It is sometimes misdiagnosed as a cyst.

It is fairly uncommon, but It is seen more in young people. Two thirds of the cases are found in females.

Warts are typically small, rough, and hard growths that are similar in color to the rest of the skin. They typically do not result in symptoms except when on the bottom of the feet where they may be painful. While they usually occur on the hands and feet they can also affect other locations. One or many warts may appear. They are not cancerous.

Warts are caused by infection with a type of human papillomavirus (HPV). Factors that increase the risk include use of public showers, working with meat, eczema, and a low immune system. The virus is believed to enter the body through skin that has been damaged slightly. A number of types exist including: common warts, plantar warts, filiform warts, and genital warts. Genital warts are often sexually transmitted.

Without treatment, most types of warts resolve in months to years. A number of treatments may speed resolution including salicylic acid applied to the skin and cryotherapy. In those who are otherwise healthy they do not typically result in significant problems. Treatment of genital warts differs from that of other types.

Warts are very common, with most people being infected at some point in their life. The estimated current rate of non-genital warts among the general population is 1–13%. They are more common among young people. Estimated rates of genital warts in sexually active women is 12%. Warts have been described at least as far back as 400 BC by Hippocrates.

A range of types of wart have been identified, varying in shape and site affected, as well as the type of human papillomavirus involved. These include:

- Common wart ("Verruca vulgaris"), a raised wart with roughened surface, most common on hands, but can grow anywhere on the body. Sometimes known as a Palmer wart or Junior wart.

- Flat wart ("Verruca plana"), a small, smooth flattened wart, flesh-coloured, which can occur in large numbers; most common on the face, neck, hands, wrists and knees.

- Filiform or digitate wart, a thread- or finger-like wart, most common on the face, especially near the eyelids and lips.

- Genital wart (venereal wart, "Condyloma acuminatum", "Verruca acuminata"), a wart that occurs on the genitalia.

- Mosaic wart, a group of tightly clustered plantar-type warts, commonly on the hands or soles of the feet.

- Periungual wart, a cauliflower-like cluster of warts that occurs around the nails.

- Plantar wart (verruca, "Verruca plantaris"), a hard sometimes painful lump, often with multiple black specks in the center; usually only found on pressure points on the soles of the feet.

Erythroplasia of Queyrat is a squamous-cell carcinoma of the glans penis (head of the penis) or inner prepuce (foreskin) in males, and the vulvae in females. It mainly occurs in uncircumcised males, over the age of 40. Erythroplasia of Queyrat may also occur on the anal mucosa or the oral mucosa.

Some sources state that this condition is synonymous with Bowen's disease, however generally speaking Bowen's disease refers to carcinoma in situ of any location on the skin such as the lower leg. Like Bowen's disease, erythroplasia of Queyrat is associated with human papillomavirus 16 and is a precursor for invasive squamous-cell carcinoma.

It is named for French dermatologist Louis Queyrat (1856-1933), who was head of the dermatology service of l'Hôpital Ricord, a venereal hospital in Paris, now Hôpital Cochin.