By Eduardo Gonzales, MD
Q. Are there vaccines available that can prevent cancers?
A. Yes, there are vaccines that can prevent cancers, but they prevent only those that are caused by cancer-causing viruses. The cancer-causing viruses, of which there are but a handful, play a major role in the development of certain cancers, although in many cases, indirectly.
The viruses that are associated with cancers include hepatitis B and C viruses (HBV and HCV), human papilloma viruses (HPV), human T-cell leukemia virus (HTLV-1), human immunodeficiency virus (HIV), Epstein-Barr virus (EBV), human herpes virus 8 (HHV-8) which is also known as Kaposi sarcoma-associated herpes virus (KSHV), and Merkel cell polyomavirus (MCV).
The hepatitis B and C viruses can give rise to chronic hepatitis B and C, respectively, conditions that lead to cirrhosis or severe scarring of the liver, which in turn predisposes one to liver cancer. Eighty percent of all liver cancers are preceded by cirrhosis while the lifetime risk of cancer of the liver among chronic carriers of Hepatitis B virus is up to 100 times higher than the rest of the population.
The human papilloma viruses (HPV) constitute a large group of more than 100 viruses. Most of these viruses are either harmless or cause benign diseases like skin warts. But a few, especially those that are sexually transmitted, are linked to the development of cancers of the cervix, anus, and the female genital area. In fact, almost all females with cervical cancers have previously been infected with an HPV.
HTLV-1 has been established as the cause of a form of leukemia in adults, but only one to four percent of people who get infected with the virus develop leukemia.
HIV (the virus that causes AIDS) increases one’s risk of developing lymphomas, Kaposi’s sarcoma, cervical cancer in women, and anal cancer.
The Epstein-Barr virus (EBV) causes infectious mononucleosis, which is also referred to as “kissing disease,” a self-limiting illness that is characterized by pharyngitis and enlargement of the lymph nodes, spleen, and liver. Overall, very few people who had been infected with EBV will ever develop cancer. In any case, the cancers that are associated with EBV are nasopharyngeal cancer (cancer of the area in the back of the nose), certain types of lymphomas such as Burkitt lymphoma and Hodgkin lymphoma, and some cancers of the stomach, thymus, salivary glands, and urogenital system.
The human herpes virus 8 (HHV-8) on the other hand, may cause Kaposi’s lymphoma under conditions of immune deficiency.
Merkel cell polyomavirus (MCV) infection is a very common illness that generally causes no symptoms. But in a few people, the infection gives rise to Merkel cell cancer, a rare, aggressive malignancy that commonly involves the skin, but can subsequently metastasize to lymph nodes and other organs. About eight out of 10 Merkel cell cancers are now thought to be linked to MCV infection.
VACCINES AGAINST CANCER-CAUSING VIRUSES CAN PROTECT MANY PEOPLE
At present, there are vaccines for only two of the cancer-causing viruses, hepatitis B and HPV, but if administered to their target population, these two vaccines can prevent countless cancer deaths among Filipinos because liver cancer and cervical cancer, the malignancies indirectly targeted by the vaccines, are very prevalent in the Philippines. Liver cancer, which is only the world’s eighth most common cancer, is the third most common malignancy—second most common in men and sixth in women—in our country. In 2014, liver cancer claimed the lives of 20 Filipinos a day, a number that is projected to double by 2030. Cervical cancer, on the other hand, is the second most common cancer in women in the Philippines. In 2010, experts’ estimates are that 12 Filipino women died of cervical cancer every day.
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Tags: cancer-causing, cervical cancer, Eduardo Gonzales, Epstein-Barr virus, human herpes virus, human immunodeficiency virus, human papilloma viruses, liver cancer, Medical Notes, Merkel cell cancer, Merkel cell polyomavirus, nasopharyngeal cancer, Vaccines that can prevent cancers