Cancer

“Cold tumor” and “Hot tumor” are terms that indicate the immune response status of a tumor. In the case of most solid cancers, they refer to the state of a tumor being “Cold” or “Hot” in terms of immune recognition and infiltration. A “Cold tumor” is one where immune cells, particularly T cells, fail to infiltrate the tumor effectively, leading to a lack of immune activation. This makes it difficult to achieve therapeutic effects with immune checkpoint inhibitors, which aim to activate the immune response against the tumor. Conversely, a “Hot tumor” signifies a tumor in which immune cells successfully infiltrate, leading to an activated immune response within the tumor microenvironment.

Hot tumors tend to exhibit higher response rates to immune checkpoint inhibitors, making the conversion from a Cold tumor to a Hot tumor a key aspect of cancer treatment.

To treat solid tumors, two barriers need to be overcome: physical and immune barriers.

In the case of solid tumors, cancer cells manipulate the tumor microenvironment and surrounding fibrous tissue to their advantage, promoting their growth. The area around cancer cells becomes enriched with extracellular matrix (ECM), creating a physically challenging environment that hinders penetration of external cells and drugs. Even if immune cells (T cells) manage to infiltrate, the closed microenvironment within solid tumors, characterized by low pH, insufficient nutrients, and oxygen, makes activating immune responses difficult. Furthermore, due to the influence of surrounding cells, an immune-suppressive environment is formed around solid tumors, making it hard for T cells to activate from the outside. Overcoming these limitations requires the development of third-generation immunotherapies that can surmount these obstacles.