micro 19.5

What is cancer?

A disease caused by the loss of normal cell-cycle regulation, resulting in uncontrolled cell proliferation.

What is a tumor?

An abnormal mass of cells that can be either benign or malignant.

What is the difference between a benign and malignant tumor?

A benign tumor is not cancerous, while a malignant tumor is cancerous.

What happens to cells when they lose control of their cell cycle?

They rapidly divide, may lose normal differentiation, and can lose contact inhibition, allowing them to grow on top of one another.

What are traditional treatments for cancer?

Radiation and chemotherapy.

Why can radiation and chemotherapy have unwanted side effects?

They can damage normal cells as well as cancer cells.

How can the immune system respond to cancer cells?

It can recognize and destroy abnormal cancer cells.

Why can cancer cells become targets of adaptive immunity?

Many cancer cells lack the normal complement of self-proteins and may display abnormal tumor antigens.

What are tumor antigens?

Antigens found on abnormal cancer cells that can be recognized by the immune system.

Why can tumor antigens stimulate an immune response even though they may be self-antigens?

Tumor antigens are not necessarily encountered during the normal process that eliminates self-reactive lymphocytes during development.

What cytokine can stimulate naïve helper T cells to differentiate into TH1 cells during an antitumor response?

IL-12.

What do TH1 cells do during an immune response against tumors?

They release cytokines that activate NK cells and enhance cytotoxic T-cell killing.

Which two major immune cells can directly kill cancer cells?

Natural killer (NK) cells and cytotoxic T cells.

How do NK cells and cytotoxic T cells kill cancer cells?

They induce apoptosis through the actions of perforins and granzymes.

What do perforins do?

They help create pores in the target cell membrane, allowing granzymes to enter.

What do granzymes do?

They activate pathways that cause apoptosis of the target cell.

What is the CD95 (Fas) cytotoxic pathway?

A second mechanism by which activated cytotoxic T cells induce apoptosis in abnormal cells.

How does the CD95 (Fas) pathway cause cancer-cell death?

Cytotoxic T cells bind CD95 (Fas) on abnormal cells, triggering apoptosis.

Why does cancer remain a common cause of death despite immune defenses against tumors?

Malignant tumors can actively suppress immune responses and develop mechanisms that allow them to escape immune destruction.

How can cancer cells suppress cytotoxic T cells?

They can express membrane proteins that shut off cytotoxic T-cell activity.

How can cancer cells suppress immune responses through regulatory T cells?

Cancer cells can induce regulatory T cells, which suppress immune responses.

What are the two types of cancer vaccines?

Preventive vaccines and therapeutic vaccines.

What is the purpose of a preventive cancer vaccine?

To prevent cancer from developing by preventing infections known to cause cancer.

What are two examples of preventive cancer vaccines?

Vaccines against human papillomavirus (HPV) and hepatitis B virus (HBV).

What cancers can HPV and hepatitis B vaccines help prevent?

HPV vaccines help prevent cervical cancer, while hepatitis B vaccines help prevent liver cancer.

What is the purpose of a therapeutic cancer vaccine?

To treat an existing cancer by stimulating the immune system to attack tumor cells.

How do therapeutic cancer vaccines use tumor-specific antigens?

They stimulate the immune system to selectively target cancer cells.

What was the first FDA-approved therapeutic cancer vaccine, and what did it treat?

Sipuleucel-T (Provenge), approved in 2010 to treat certain cases of prostate cancer.

How does sipuleucel-T work?

The patient's antigen-presenting cells are removed, cultured with a tumor-specific molecule, and returned to the patient to enhance the immune response against cancer.

What is T-VEC (talimogene laherparepvec), and how does it work?

A therapeutic vaccine approved for melanoma that uses a modified virus injected into tumors to infect and lyse tumor cells while stimulating a broader antitumor immune response.