**4. Cancer**

Cancer is a broad term for a class of diseases characterized by uncontrolled growth and proliferation of abnormal cells. These normal cells have the ability to infiltrate and destroy normal tissues. The types of treatments that one receives depend on the type of cancer and how advanced it is. Mostly it is a combination of treatments such as chemotherapy, radiotherapy, immunotherapy, hormonal therapy, stem cell transplantation and other targeted therapies. Cancer on its own and its treatment using chemotherapy or radiotherapy weakens one's immune system, reducing the number of infections fighting immune cells and making it harder for one's body to fight infections including the viral infections. And this is why cancer patients who are undergoing or recently underwent chemo/radiotherapy are particularly at higher risk.
