While each type of cancer has its own distinctive symptoms, most of them can indicate their presence by the occurrence and the prolonged presence of any common symptom. Some of the general symptoms of cancer in cats are:

- Any lump that changes shape or size

- Any sore that does not heal

- Change in bowel or bladder habits

- Difficulty eating or swallowing

- Difficulty urinating or defecating

- Unexplained bleeding or discharge from body

- Loss of appetite

- Chronic weight loss

- Coughing or difficulty breathing

- Stiffness

- Oral odor

Note that ravenous hunger, while a sign of other diseases like hyperthyroid, can also be a sign of cancer.

Although cats are diagnosed with cancer at lower rates than dogs or humans, the types of cancer and symptoms are identical. Cancer in cats can occur in any location or body system, and most symptoms can be detected externally. However, to reach a definitive diagnosis, further tests such as blood and urine tests, cytology, and biopsy are required. Due to the excessively aggressive nature of cancer in cats, it is advisable for owners to take their cat to a veterinarian for an examination following occurrence of any symptom to prevent spreading.

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

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.

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.

Basal-cell skin cancer (BCC) usually presents as a raised, smooth, pearly bump on the sun-exposed skin of the head, neck or shoulders. Sometimes small blood vessels (called telangiectasia) can be seen within the tumor. Crusting and bleeding in the center of the tumor frequently develops. It is often mistaken for a sore that does not heal. This form of skin cancer is the least deadly and with proper treatment can be completely eliminated, often without scarring.

The most common cancers in children are (childhood) leukemia (32%), brain tumors (18%), and lymphomas (11%). In 2005, 4.1 of every 100,000 young people under 20 years of age in the U.S. were diagnosed with leukemia, and 0.8 per 100,000 died from it. The number of new cases was highest among the 1–4 age group, but the number of deaths was highest among the 10–14 age group.

In 2005, 2.9 of every 100,000 people 0–19 years of age were found to have cancer of the brain or central nervous system, and 0.7 per 100,000 died from it. These cancers were found most often in children between 1 and 4 years of age, but the most deaths occurred among those aged 5–9. The main subtypes of brain and central nervous system tumors in children are: astrocytoma, brain stem glioma, craniopharyngioma, desmoplastic infantile ganglioglioma, ependymoma, high-grade glioma, medulloblastoma and atypical teratoid rhabdoid tumor.

Other, less common childhood cancer types are:

- Neuroblastoma (6%, nervous system)

- Wilms tumor (5%, kidney)

- Non-Hodgkin lymphoma (4%, blood)

- Childhood rhabdomyosarcoma (3%, many sites)

- Retinoblastoma (3%, eye)

- Osteosarcoma (3%, bone cancer)

- Ewing sarcoma (1%, many sites)

- Germ cell tumors (5%, many sites)

- Pleuropulmonary blastoma (lung or pleural cavity)

- Hepatoblastoma and hepatocellular carcinoma (liver cancer)

There are a variety of different skin cancer symptoms. These include changes in the skin that do not heal, ulcering in the skin, discolored skin, and changes in existing moles, such as jagged edges to the mole and enlargement of the mole.

Childhood cancer (also known as pediatric cancer) is cancer in a child. In the United States, an arbitrarily adopted standard of the ages used are 0–14 years inclusive, that is, up to 14 years 11.9 months of age. However, the definition of childhood cancer sometimes includes adolescents between 15–19 years old. Pediatric oncology is the branch of medicine concerned with the diagnosis and treatment of cancer in children.

Worldwide, it is estimated that childhood cancer has an incidence of more than 175,000 per year, and a mortality rate of approximately 96,000 per year. In developed countries, childhood cancer has a mortality of approximately 20% of cases. In low resource settings, on the other hand, mortality is approximately 80%, or even 90% in the world's poorest countries. In many developed countries the incidence is slowly increasing, as rates of childhood cancer increased by 0.6% per year between 1975 and 2002 in the United States and by 1.1% per year between 1978 and 1997 in Europe.

Throat cancer usually begins with symptoms that seem harmless enough, like an enlarged lymph node on the outside of the neck, a sore throat or a hoarse sounding voice. However, in the case of throat cancer, these conditions may persist and become chronic. There may be a lump or a sore in the throat or neck that does not heal or go away. There may be difficult or painful swallowing. Speaking may become difficult. There may be a persistent earache. Other possible but less common symptoms include some numbness or paralysis of the face muscles.

Presenting symptoms include :

- Mass in the neck

- Neck pain

- Bleeding from the mouth

- Sinus congestion, especially with nasopharyngeal carcinoma

- Bad breath

- Sore tongue

- Painless ulcer or sores in the mouth that do not heal

- White, red or dark patches in the mouth that will not go away

- Earache

- Unusual bleeding or numbness in the mouth

- Lump in the lip, mouth or gums

- Enlarged lymph glands in the neck

- Slurring of speech (if the cancer is affecting the tongue)

- Hoarse voice which persists for more than six weeks

- Sore throat which persists for more than six weeks

- Difficulty swallowing food

- Change in diet or weight loss

Most cases (80%) of squamous cell carcinoma attributed to ultraviolet radiation present in areas of the skin that are usually more exposed to sunlight (e.g., head, face, neck). Although a particular form of squamous cell carcinoma, Kangri cancer is more often associated with the abdomen, thigh, and leg regions due to the usage and positioning of kangri pots, which come in close contact with these anatomical features.

Over time, the use of Kangri pots to keep warm results in erythema ab igne, a precancerous keratotic growth that “take the shape of superficial, serpegenous, reticular blackish brown colored lesions.” Eventually, the cells at the lesion site become more irregular in shape and form; the lesions “ulcerate” and may become itchy and bloody. The resulting irregular growth is the presentation of Kangri cancer.

The possible signs of oropharyngeal cancer are:

- A sore throat that persists

- Pain or difficulty with swallowing

- Unexplained weight loss

- Voice changes

- Ear pain

- A lump in the back of the throat or mouth

- A lump in the neck

- A dull pain behind the sternum

- Cough

Kangri cancer is a type of squamous-cell carcinoma of the skin. It is found only in Kashmir in the northwest of the Indian subcontinent. It occurs on the lower abdomen and inner thighs and is due to the use of a kangri, a baked clay pot weaved around with wicker-work, used as a source for warmth by people in Kashmir during cold weather. One of the earliest records of the condition was described in 1881 by surgeons at the Kashmir Mission Hospital and its cause was recognized in the early 20th century as described by Arthur Neve.

Despite current knowledge of the cause of this condition, cases are still being reported.

Other conditions associated with prolonged use of the kangri in this fashion include erythema ab igne, a reticulate hypermelanosis with erythema.

Squamous cell cancers are common in the mouth, including the inner lip, tongue, floor of mouth, gingivae, and hard palate. Cancers of the mouth are strongly associated with tobacco use, especially use of chewing tobacco or "dip", as well as heavy alcohol use. Cancers of this region, particularly the tongue, are more frequently treated with surgery than are other head and neck cancers.

Surgeries for oral cancers include

- Maxillectomy (can be done with or without orbital exenteration)

- Mandibulectomy (removal of the mandible or lower jaw or part of it)

- Glossectomy (tongue removal, can be total, hemi or partial)

- Radical neck dissection

- Mohs procedure

- Combinational e.g., glossectomy and laryngectomy done together.

The defect is typically covered/improved by using another part of the body and/or skin grafts and/or wearing a prosthesis.

Oropharyngeal cancer is a disease in which cancer form in the tissues of the throat (oropharynx). The oropharynx is the middle part of the throat that includes the base of the tongue, the tonsils, the soft palate, and the walls of the pharynx. Oropharyngeal cancers can be divided into two types, HPV-positive, which are related to human papillomavirus infection, and HPV-negative cancers, which are usually linked to alcohol or tobacco use.

Symptoms of Hypopharyngeal Cancer include:

- Swollen lymph nodes in the neck (first sign of a problem in half of all patients)

- Sore throat in one location that persists after treatment

- Pain that radiates from the throat to the ears

- Difficult or painful swallowing (often leads to malnutrition and weight loss because of a refusal to eat)

- Voice changes (late stage cancer)

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.

In its early stages, it can go unnoticed. It can be painless with slight physical changes. But the precursor tissue changes, can be noticed by the doctors.

Early stage symptoms can include persistent red or white patches, a non-healing ulcer, progressive swelling or enlargement, unusual surface changes, sudden tooth mobility without apparent cause, unusual oral bleeding or epitaxis and prolonged hoarseness.

Late stage symptoms can include an indurated area, paresthesia or dysesthesia of the tongue or lips, airway obstruction, chronic serous otitis media, otalgia, trismus, dysphagia, cervical lymphadenopathy, persistent pain or referred pain and altered vision.

Esophageal cancer may be due to either squamous cell carcinoma (ESCC) or adenocarcinoma (EAC). SCCs tend to occur closer to the mouth, while adenocarcinomas occur closer to the stomach. Dysphagia (difficulty swallowing, solids worse than liquids) and painful swallowing are common initial symptoms. If the disease is localized, surgical removal of the affected esophagus may offer the possibility of a cure. If the disease has spread, chemotherapy and radiotherapy are commonly used.

Ninety percent of cases of head and neck cancer (cancer of the mouth, nasal cavity, nasopharynx, throat and associated structures) are due to squamous cell carcinoma.

The symptoms produced by metastatic breast cancer vary by the location of the metastases. For instance:

- Metastatic disease to the bone causes severe, progressive pain, and, less commonly, pathological fracture, erythema over the affected bone, and swelling.

- Metastatic breast cancer to the brain causes the following symptoms: persistent, progressively worsening headache, visual changes, seizures, nausea or vomiting, vertigo, behavioral and personality changes, and increased intracranial pressure.

- Metastatic disease to the liver causes jaundice, elevated liver enzymes, abdominal pain, loss of appetite, nausea, and vomiting

- Metastatic breast cancer to the lung or pleura causes chronic cough, dyspnea, abnormal chest X-ray, and chest pain.

- Other nonspecific systemic symptoms of metastatic breast cancer include fatigue, malaise, weight loss, and poor appetite.

The first noticeable symptom of breast cancer is typically a lump that feels different from the rest of the breast tissue. More than 80% of breast cancer cases are discovered when the woman feels a lump. The earliest breast cancers are detected by a mammogram. Lumps found in lymph nodes located in the armpits can also indicate breast cancer.

Indications of breast cancer other than a lump may include thickening different from the other breast tissue, one breast becoming larger or lower, a nipple changing position or shape or becoming inverted, skin puckering or dimpling, a rash on or around a nipple, discharge from nipple/s, constant pain in part of the breast or armpit, and swelling beneath the armpit or around the collarbone. Pain ("mastodynia") is an unreliable tool in determining the presence or absence of breast cancer, but may be indicative of other breast health issues.

Inflammatory breast cancer is a particular type of breast cancer which can pose a substantial diagnostic challenge. Symptoms may resemble a breast inflammation and may include itching, pain, swelling, nipple inversion, warmth and redness throughout the breast, as well as an orange-peel texture to the skin referred to as "peau d'orange". As inflammatory breast cancer does not present as a lump there can sometimes be a delay in diagnosis.

Another reported symptom complex of breast cancer is Paget's disease of the breast. This syndrome presents as skin changes resembling eczema, such as redness, discoloration, or mild flaking of the nipple skin. As Paget's disease of the breast advances, symptoms may include tingling, itching, increased sensitivity, burning, and pain. There may also be discharge from the nipple. Approximately half of women diagnosed with Paget's disease of the breast also have a lump in the breast.

In rare cases, what initially appears as a fibroadenoma (hard, movable non-cancerous lump) could in fact be a phyllodes tumor. Phyllodes tumors are formed within the stroma (connective tissue) of the breast and contain glandular as well as stromal tissue. Phyllodes tumors are not staged in the usual sense; they are classified on the basis of their appearance under the microscope as benign, borderline, or malignant.

Occasionally, breast cancer presents as metastatic disease—that is, cancer that has spread beyond the original organ. The symptoms caused by metastatic breast cancer will depend on the location of metastasis. Common sites of metastasis include bone, liver, lung and brain. Unexplained weight loss can occasionally signal breast cancer, as can symptoms of fevers or chills. Bone or joint pains can sometimes be manifestations of metastatic breast cancer, as can jaundice or neurological symptoms. These symptoms are called "non-specific", meaning they could be manifestations of many other illnesses.

Most symptoms of breast disorders, including most lumps, do not turn out to represent underlying breast cancer. Fewer than 20% of lumps, for example, are cancerous, and benign breast diseases such as mastitis and fibroadenoma of the breast are more common causes of breast disorder symptoms. Nevertheless, the appearance of a new symptom should be taken seriously by both patients and their doctors, because of the possibility of an underlying breast cancer at almost any age.

Signs and symptoms which may suggest lung cancer include:

- Respiratory symptoms: coughing, coughing up blood, wheezing, or shortness of breath

- Systemic symptoms: weight loss, weakness, fever, or clubbing of the fingernails

- Symptoms due to the cancer mass pressing on adjacent structures: chest pain, bone pain, superior vena cava obstruction, or difficulty swallowing

If the cancer grows in the airways, it may obstruct airflow, causing breathing difficulties. The obstruction can lead to accumulation of secretions behind the blockage, and predispose to pneumonia.

Depending on the type of tumor, paraneoplastic phenomena—symptoms not due to the local presence of cancer—may initially attract attention to the disease. In lung cancer, these phenomena may include hypercalcemia, syndrome of inappropriate antidiuretic hormone (SIADH, abnormally concentrated urine and diluted blood), ectopic ACTH production, or Lambert–Eaton myasthenic syndrome (muscle weakness due to autoantibodies). Tumors in the top of the lung, known as Pancoast tumors, may invade the local part of the sympathetic nervous system, leading to Horner's syndrome (dropping of the eyelid and a small pupil on that side), as well as damage to the brachial plexus.

Many of the symptoms of lung cancer (poor appetite, weight loss, fever, fatigue) are not specific. In many people, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention. Symptoms that suggest the presence of metastatic disease include weight loss, bone pain and neurological symptoms (headaches, fainting, convulsions, or limb weakness). Common sites of spread include the brain, bone, adrenal glands, opposite lung, liver, pericardium, and kidneys. About 10% of people with lung cancer do not have symptoms at diagnosis; these cancers are incidentally found on routine chest radiography.

Penile cancer arises from precursor lesions, which generally progress from low-grade to high-grade lesions. For HPV related penile cancers this sequence is as follows:

- A. Squamous hyperplasia;

- B. Low-grade penile intraepithelial neoplasia (PIN);

- C. High-grade PIN (carcinoma in situ—Bowen's disease, Erythroplasia of Queyrat and bowenoid papulosis (BP));

- D. Invasive Carcinoma of the Penis.

However, in some cases non-dysplastic or mildly dysplastic lesions may progress directly into cancer. Examples include flat penile lesions (FPL) and condylomata acuminata.

In HPV negative cancers the most common precursor lesion is lichen sclerosus (LS).

Urachal cancer can exist for some years without any symptoms. The most frequent initial symptom is haematuria which occurs when the urachal tumour has penetrated the bladder wall, but mucinuria (mucin in the urine), local pain or swelling, recurrent local or urinary tract infections and umbilical discharge can (but is not always) be seen.