Cancer is a broad class of diseases involving uncontrollable cell growth. Cancerous cells rapidly divide and grow, producing masses of tissue called tumors. While benign tumors cannot metastasize, or invade neighboring tissue, and some are relatively harmless, malignant tumors can spread throughout the body, destroying healthy tissue and interfering with regular bodily function. There are over 200 different cancers, which originate from different cells in different organs throughout the body. Cancers are largely defined by their tissue of origin, or the cells of the organ from which the tumor originates. This extraordinary diversity is one of the reasons that it remains so difficult to understand, prevent, diagnose, and trecat cancer.

The causes of cancer are complex and not fully understood. Some cancers can be traced directly to inherited genetic traits, but many cannot. A wide range of environmental, dietary, and behavioral factors, as well as some infections, are known to increase the risk of developing cancer. The most significant risk factor for cancer is old age.

Cancer is a relatively common disease–in 2021, there were more than 17.4 million people living with cancer in the United States. It is estimated that over 2 million Americans were diagnosed with cancer in 2024 alone. While the number of new cases of cancer has increased over the last few decades, largely due to an aging population and enhanced screening for common cancers, advances in treatment have significantly improved survival rates.

Today, the five-year survival rate for adults with cancer is more than 69 percent. In other words, 69 percent of adults are living five years or more after their initial diagnosis, up from 50 percent in 1975. For childhood cancers, the five-year survival rate is 85 percent, up from 58 percent in 1975–77.

For information regarding the most up to date statistics on cancer incidence and mortality rates, survival rates, and information about cancer by age, sex, or race/ethnicity, visit the National Cancer Institute’s Surveillance Epidemiology and End Results (SEER) Cancer Stat Facts or American Cancer Society’s annual fact sheet.

For more specific information on different types of cancer, visit http://www.oncolink.org/types/