How many cancer cells do you need to get cancer?

The number of cancer cells required to cause cancer, or the threshold required for tumor formation, can vary depending on several factors, including the type of cancer, the individual's immune response, and other genetic and environmental factors. It's not a simple matter of counting the number of cancerous cells. Rather, tumor formation and progression involve complex interactions between cancer cells and the body's response to them.

In general, a single cancerous cell is not enough to establish a tumor. Most often, it takes the accumulation of multiple genetic mutations and altered behaviors within cells for them to become cancerous and overcome the body's natural defenses. The process of cancer development and growth is usually gradual and can take years or even decades.

Furthermore, even if a group of cancer cells arises, the body's immune system may be able to detect and eliminate them before they become a noticeable tumor. This ability of the immune system to eliminate abnormal or cancerous cells is known as immune surveillance.

Therefore, there's no specific threshold number of cancer cells that define the development of cancer, but rather a complex process of accumulated genetic alterations and interactions with the host environment. Additionally, every individual's response to cancer cells can vary, influenced by their unique genetics, lifestyle factors, and overall health conditions.