Understanding If Cancer Is Contagious

A Common Question With Uncommon Considerations

Cancer is not contagious in the conventional sense and is not considered an infectious or communicable disease. Cancer itself cannot be transmitted from one person to another (unlike some animals) by breathing the same air, sharing a toothbrush, touching, kissing, or having sex. With a few rare exceptions (organ transplant recipients, mother to fetal transmission, and a few rare events), the immune system will recognize any foreign cells (including cancer cells from another person) and destroy them.

Some infections that can be transmitted (including some sexually transmitted diseases), however, may increase the risk of developing cancer. In addition, cancer may run in families, but instead of being transmitted, this risk is related to genetic traits (a genetic predisposition) or common exposures that increase risk.

Mature ethnic woman with cancer wearing headwrap on couch
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Contagiousness and Cancer

Since cancer can be contagious in some species, wondering why it is not in humans is a good question that can be looked at in a few different ways.

The first way to look at this is by visualizing what happens if a cancer cell from another person were to enter our body (it would have to be directly transmitted since cancer cells can't live outside the body). This is what former Venezuelan president Hugo Chavez claimed when he stated that his enemies gave him cancer.

In an unethical experiment conducted in the 1950s and 1960s, two New York researchers actually did some experiments in which they injected cancer cells into healthy prisoners and cancer patients (the recipients were not informed of this experiment) to see if he could "cause" cancer. With only one exception, the recipient's immune system fought off the cancer cells before they passed beyond the nodule stage.

Our immune cells see cancer cells from another person as they would see disease-causing viruses or bacteria.

(In the study, the experiment was justified by the researchers who hoped to discover ways to build an immunity to cancer, and was funded by the American Cancer Society and the U.S. Public Health Service). In one other human experiment, melanoma cells were transferred from a person to his mother to try to induce immunity to cancer, and the mother died from melanoma.

There are a few other very rare exceptions, for example, a 2015 report in The New England Journal of Medicine describes how cancer cells from a tapeworm invaded a man's body spreading to several lymph nodes and his lungs. While ordinarily, the immune system would not allow this, the man was severely immunosuppressed due to HIV/AIDS. There have also been rare cases in which cancer has been transmitted (via a needle poke or a cut on the hand) to a lab worker and a surgeon (sarcoma). In these cases, however, while the cancer cells grew locally where they entered the body, but they did not progress beyond the site of entry.

The lack of contagiousness of cancer is also better understood when looking at how cancer develops. Cancer cells arise after a series of mutations (in genes that control the growth of the cell) lead to uncontrolled growth of the cell. Even when genetic damage occurs, the human body has genes (such as tumor suppressor genes) that code for proteins designed to either repair damaged DNA or eliminate damaged cells.

Further support for the lack of contagiousness is the lack of epidemics. In addition, oncologists and other health professionals who are exposed to large numbers of people with cancer are not any more likely to develop the disease.

Further support for the lack of contagiousness is the lack of epidemics. In addition, oncologists and other health professionals who are exposed to large numbers of people with cancer are not any more likely to develop the disease.

Organ Transplants

As noted above, cancer cells from another person that enters our bodies are destroyed by the immune system. As an exception to this general rule, there have been cases of cancer being transmitted from one person to another via organ transplant, and it's thought that transfusion-related cancer may occur in roughly 3 in 5,000 transplant recipients.

With organ transplants, there are two factors that contribute to this risk. One is that instead of just a few cancer cells (such as with a needle stick) a large volume of tumor cells are implanted in a person (from a mass in the transplanted organ). In addition, these people are usually severely immunocompromised due to the medications used to prevent rejection.

There is no evidence that cancer has ever been transmitted via blood transfusion. Despite this, there are limitations on when people with cancer can donate blood.

Mother to Child Transmission

There are a few reported cases of cancer transmission during pregnancy, and this may occur in three ways.

  • From the mother to the baby: While tumors may spread to the placenta, the placenta usually prevents cancer cells from reaching the baby. The chance of cancer being transmitted (1 in 1,000 pregnant women are thought to have cancer) is estimated at only 0.000005 percent. Transmission is most common with leukemia/lymphomas and melanoma.
  • Twin to twin transmission of leukemia: Again, transmission is very rare, but may occur at times.
  • Choriocarcinoma: Choriocarcinoma is a rare tumor that arises in the placenta. The tumor may spread to both the mother and the baby and is the only case of serial transmission of cancer (from the placenta to the mother, and then from the mother to recipients of organs donated by that mother).

Contagious Cancers in Other Species

Cancer has now been found to be transmitted among members of eight different species. It's thought that the reason this may occur, unlike in humans, is due to a lack of genetic diversity (genetic inbreeding) so that the cancer cells from another member of that species are not recognized as abnormal. These include:

  • Dogs: Canine transmissible venereal tumor may be transmitted sexually or through direct blood contact.
  • Tasmanian devils: Tasmanian devils facial tumor may be transmitted from one animal to another by biting.
  • Bivalves: Leukemia may be transmitted in four different species of bivalves, possibly through filter feeding.
  • Hamsters: There are also reports of transmission of reticulum cell sarcoma between hamsters in older studies, as well as the possibility of mosquitoes being a vector in transmission.

Infections Associated With Cancer

Some infections that can be passed from person to person are thought to lead to cancer. In these cases, however, it's not cancer per se that is contagious, but rather the infection that may or may not (and in most cases does not) lead to cancer.

Infections with these microorganisms are common, whereas the cancers that arise as a result of the infections are not. In addition, most cancers are multifactorial in origin (have many causes), and other factors such as exposure to carcinogens, immunosuppression, genetic factors, lifestyle, and more may combine with the infection to induce cancer.

Infections may lead to cancer in different ways. Some may cause inflammation that leads to cancer (due to increased cell division of cells involved in repair), whereas others may cause immunosuppression. Yet others may damage DNA (cause mutations) directly.

In the United States, it's thought that roughly 10 percent of cancers are related to infectious diseases, though that number rises to around 25 percent worldwide.

Viruses associated with cancer include:

  • Human papillomavirus (HPV): HPV is the most common sexually transmitted disease, and has been linked with cervical cancer, anal cancer, penile cancer, vaginal cancer, and head and neck cancers. In most cases, infection with HPV goes away on its own, but when persistent, may lead to inflammation and cancer. Not all strains of HPV are linked with cancer.
  • Hepatitis B virus and hepatitis C virus: Both hepatitis B and C are associated with liver cancer, and together are the greatest cause of liver cancer worldwide.
  • Epstein Barr virus (EBV): EBV is best known for being the cause of mononucleosis, though it has been linked to several cancers as well. It's thought that it may play a role in 40 percent to 50 percent of Hodgkin's lymphomas. While rare in the U.S., it is also associated with Burkitt's lymphoma, nasopharyngeal carcinoma, gastric adenocarcinoma, and more. While 90 percent of people are thought to be infected, only a relatively small number develop cancer.
  • HIV/AIDS: There are several types of cancer associated with HIV/AIDS, related to immunosuppression.
  • Human herpesvirus Type 8 (HHV-8) or Kaposi sarcoma herpes virus most commonly leads to Kaposi's sarcoma in people with HIV.
  • Human T-lymphotropic virus-1 (HTLV-1): HTLV-1 is associated with some leukemias and lymphomas, but while infection is relatively common, cancers are not.
  • Merkel cell polyomavirus: The Merkel cell polyomavirus is very common worldwide, but only rarely leads to a type of skin cancer called Merkel cell carcinoma.

Bacteria associated with cancer include:

  • H. pylori: H. pylori infection is associated with stomach cancer, as well as peptic ulcer disease.

Parasites associated with cancer include:

  • Liver flukes: Two different liver flukes are linked with bile duct cancer and found primarily in East Asia.
  • Schistosomiasis: The worm that causes this disease is associated with bladder cancer.

In addition to these specific organisms, microorganisms on or in our bodies may be associated with either an increased or decreased risk of cancer. For example, the microbiome of the skin (normal bacteria that live on the skin) may be associated with the development of skin cancer, and good gut bacteria may lower lymphoma risk.

Cancers That Run in Families

Genetics play a role in cancers that might seem to be contagious (they run in families), but despite this clustering of cancers, the cancers are not directly passed from one person to another.

Having a genetic predisposition to cancer does not mean that a person will get cancer. Hereditary cancer accounts for roughly 10 percent of cancers overall (the influence of genetics can vary by type). Many of the gene mutations associated with cancer (such as BRCA mutations) occur in tumor suppressor genes. These genes code for proteins that repair DNA that has been damaged, or instead eliminates the cell before it becomes a cancer cell. In this case, having the mutated gene does not cause cancer, but interferes with the body's ability to repair damaged cells that have been damaged by environmental exposures and more.

Even without a genetic predisposition, cancer may appear to cluster in families. This may be due to shared lifestyle habits (such as smoking or dietary habits), exposure to similar carcinogens in the environment, such as radon exposure in the home. Cancers may also occur due to exposure to viruses (such as hepatitis B) that is transmitted between family members.

Intimacy for Those With Cancer

It's clear that cancer itself cannot be transmitted by touching, kissing, or sex, so (with the exception of a few precautions) it's usually fine to be intimate, and intimacy is actually advised.

Intimacy can not only help a friend or loved one better cope with their disease, but it can ease any feelings of isolation a person may have during cancer therapy.

For those who have infections linked with cancer, as well as those living with cancer, a few precautions are important.

Precautions to Prevent Spread of Infections Associated With Cancer

HPV can be transmitted sexually and hepatitis B and C, as well as HIV, can be transmitted sexually as well as through contact with blood. Hepatitis B is spread much more easily than HIV, and even sharing a toothbrush could lead to transmission.

Safe sex includes the use of condoms and more. Blood precautions are important with hepatitis B, C, and HIV. With hepatitis B, immunization is the best way to prevent the disease.

Sexual Precautions During Cancer Treatment

For those going through chemotherapy, precautions may need to be made to protect both partners.

People With Cancer:

  • Women who are receiving chemotherapy should use a condom, as becoming pregnant with some chemotherapy drugs is associated with birth defects.
  • Oral, vaginal, and anal sex should be avoided if either partner has open sores.
  • If your white blood count is very low (chemotherapy-induced thrombocytopenia), sex should be postponed until your white count is higher. Oncologists differ with the count they consider too low, but an absolute neutrophil count of 500 or less is sometimes used as a cutoff. The nadir period is the time when white blood cell counts are usually the lowest.
  • Both partners should wash their hands (or use hand sanitizer) before sex, and genitals should be washed before oral sex.
  • Women should urinate shortly after sex to reduce the risk of a bladder infection.
  • Water-based lubricants should be used to avoid abrasion and consequent infection risk.
  • Sex should also be avoided if your platelet count is low (chemotherapy-induced thrombocytopenia), usually defined as a platelet count less than 50,000 due to the risk of bleeding.
  • Certainly, you should avoid close contact with your partner if he or she is ill.

Loved Ones of Those With Cancer:

  • Chemotherapy drugs may be present in saliva, semen, and vaginal secretions. Your loved one's oncologist may recommend avoiding sex shortly after a chemotherapy infusion, but this can vary. Women who are or may be pregnant should talk to their partner's oncologist about possible exposure and timing.
  • With some types of radiation, such as internal radiation (brachytherapy) or radioactive iodine treatment, your radiation oncologist may recommend avoiding close contact, especially if you are pregnant.

A Word From Verywell

Cancer is not contagious and you do and should not stay away from friends or loved ones with cancer. In fact, offering your support and being near is more important than ever, and some studies have even found that better social support is linked with improved survival.

If your loved one may have a virus associated with an infectious disease, learn about the disease and any precautions you can take. You should also talk with your oncologist about any risk to you or your partner related to intimacy during treatment.

Frequently Asked Questions

  • Is cancer a disease?

    Yes, each type of cancer is considered a disease. But that's not to say that cancer is contagious. Though some cancers are associated with infections that may be contagious, cancer itself is not transmissible from one person to another.

  • How do people get cancer?

    There are many different ways people get cancer. Certain genetic mutations can cause cells to turn cancerous; these mutations can be inherited or spontaneous. Lifestyle factors can increase the chance of developing cancer, some of which include smoking, alcohol consumption, and excessive sun exposure. Some infections can also cause mutations that lead to cancer.

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