What is a Tumor, Exactly?

Published: January 7, 2020

Written by: Lukas Harnisch-Weidauer

Medically Reviewed By: Robert I. Haddad, MD

  • A tumor is any abnormal swelling within the body, but the word most often refers to a mass of cancer cells.

  • Most lumps that can be felt are not cancerous, but they should be checked out by a doctor.

  • Methods for detecting tumors include lab tests, imaging scans, and visualization with clinical instruments.

A tumor, also known as a neoplasm, is an abnormal swelling or enlargement within the body caused by cells dividing more than they should or not dying when they should. 

What is the difference between a tumor and cancer? 

Although the words “tumor” and “cancer” are often used interchangeably, they aren’t synonymous. A noncancerous (benign) tumor does not metastasize, or spread, to distant parts of the body. 

Types of benign tumors include: 

  • Osteomas, or benign bone tumors 

  • Benign brain tumors such as meningiomas and schwannomas 

  • Gland tumors such as pituitary adenomas 

  • Lymphatic tumors like angiomas. 

Most such tumors are not life-threatening, but because they can press on and interfere with surrounding organs and tissues, they generally need to be treated or removed. 

Cancerous, or malignant, tumors, by contrast, can invade nearby tissue and release cells to other parts of the body to form “secondary” tumors, or metastases. Their potential to metastasize makes such tumors especially dangerous and necessitates treatment.  

Tumors may return after treatment. If this occurs, they are called “recurrent.” 

Some tumors are classified as “pre-malignant” or “pre-cancerous” because they aren’t malignant when diagnosed, but they have the potential to become malignant in the future. Examples of pre-cancerous tumors include: 

  • Acinic-keratosis, a type of skin condition 

  • Cervical dysplasia, a lesion in the cervix 

  • Colon polyps 

What does a tumor feel like? 

Only tumors that are in the skin, in tissue just beneath the skin, or on the surface of organs palpable through the skin can be felt. The way a tumor feels depends on its size, location, type, stage, and other factors. 

A cancerous lump in the breast, for example, tends to feel firm or solid and might be fixed to underlying tissue. Such lumps are often painless but do produce pain in a small percentage of patients. Most breast lumps prove not to be cancer. 

Tumors of the thyroid gland, located at the base of the neck between the larynx and the collarbone, usually feel firmer than the rest of the gland and are usually painless. As with lumps in the breast, most thyroid lumps are not cancerous. 

The most common symptom of testicular cancer is a lump or swelling in the testicle. Such lumps can be as small as a pea and may feel like an irregular thickening of the area. The lumps are often painless. 

Some tumors are associated with other symptoms like fatigue, fever or chills, and unexplained weight loss. 

How can I tell if a lump is a tumor? 

People who feel a suspicious lump in any part of their body should have it examined by a physician. A growth could be cancerous, benign, or something else like a cyst (small sacs, usually non-cancerous, containing fluid or air). It is impossible to ultimately know what type of lump is present in the body without medical tests. 

Often, an imaging scan, such as a mammogram for breast lumps or ultrasound for thyroid lumps, can indicate whether a lump is benign or whether further tests, such as MRI or a biopsy, are necessary. In a biopsy, a clinician uses a small needle to collect fluid or tissue from a lump so it can be examined under a microscope for the presence of cancerous cells. 

How are tumors detected? 

Detection techniques vary depending on the type of tumor and its location. Tumors in the digestive tract, for example, may initially be detected with an endoscope, an instrument that can be passed through the tract and enables the physician the inner lining of various organs. Other detection techniques include imaging scans, such as: 

  • Mammographies 

  • Ultrasounds 

  • Magnetic resonance imaging (MRI) 

  • Positron emission tomography (PET) 

  • Computed tomography (CT) 

  • X-rays 

There also are a variety of lab tests that analyze blood, urine, or other bodily fluids for substances associated with different types of cancer. Ultimately, a diagnosis of cancer is made after a pathologist has viewed the cells within tissue suspected of being cancerous. 

What are the risk factors for tumors? 

Tumors can affect children and adults. There are some factors that increase the risk of developing a tumor. These include: 

  • Smoking or prolonged exposure to secondhand smoke 

  • Exposure to toxins such as benzene, or exposure to radiation 

  • Viruses like HPV 

  • Inherited conditions such as Lynch syndrome 

  • Gene mutations such as those on the BRCA gene 

If you have any of these risk factors, talk to a medical professional about ensuring proper cancer screening.  

About the Medical Reviewer


Dr Haddad received his MD Degree from St. Joseph University French School of Medicine in Beirut. He completed his residency in internal medicine at St Luke's Roosevelt Medical Center in New York City, and completed a fellowship in hematology oncology at the University of Maryland Cancer Center in Baltimore.