Cancer accounts for nearly one of every four deaths in the US, and although the incidence for certain cancers has decreased, new and more efficient therapies are certainly needed. The possibility of a larger role for cancer vaccines as a treating method remains an exciting prospect. New strategies such as using cancer vaccines in conjunction with other prescribed cancer drugs expand the potential of these compelling therapies.
Cancer vaccines fall into two categories: preventative and therapeutic. Preventative vaccines are similar to traditional vaccines, in that they aid the body in protecting itself against infection. Using today’s greater understanding of the immune system and of the antigens that tumors express, immunotherapy works to create a specific immune response that prevents or treats cancer while resulting in little to no side effects. Therapeutic, or treatment, vaccines treat cancer that has already developed by boosting a weakened immune response induced by tumor-associated antigens. Nucleic acids, synthetic peptides and proteins, microbial vectors, and actual cancer cells have all been used in cancer vaccine strategies. Treatment vaccines would work to kill cancer cells, delay/prevent growth of cancer cells, shrink tumors, or prevent a cancer from returning. In the past, it was thought that cancer vaccines would not be able to be used effectively with other treatments such as chemotherapy, but evidence is showing that concurrent therapy has been effective and included additive or synergistic effects.
As with most therapies, cancer vaccines have both advantages and disadvantages. Most have the ability to affect only tumor cells, while treatments such as chemotherapy and radiation result in the loss of normal cells as they destroy tumor cells. On the negative side, some cancer vaccines can be difficult to produce, or they may cause an adverse reaction. Typically, side effects of cancer vaccines are similar to traditional vaccines, although there can be variation among formulations and individuals. Reported side effects have included injection-site reactions, flu-like symptoms, muscle aches, fatigue, headache, breathing difficulties, and changes in blood pressure. A small number of more serious adverse reactions have been noted, though they may not have been related to a vaccine. These include asthma, pelvic inflammatory disease, appendicitis, and certain autoimmune diseases.
Today, only one therapeutic cancer vaccine, sipuleucel-T, has been approved by the FDA to treat established tumors. The vaccine is used to treat symptomatic or minimally symptomatic metastatic castrate-resistant (hormone-refractory) prostate cancer. It induces an immune response targeted against prostatic acid phosphatase, an antigen expressed in most prostate cancer. Two types of preventative cancer vaccines have been approved by the FDA (hepatitis B virus and human papillomavirus vaccines). Research is continuing with the intent of discovering more therapeutic and preventative cancer vaccines.
Clinical trials are ongoing for a number of other cancer vaccines, and most research focuses on targeting known or unknown tumor-associated antigens. It will be important to find further ways to boost the immune system and to use it to detect tumor antigens and attack tumor cells. Protein/peptide-based, vector-based, tumor cell/tumor cell-lysate, and DNA/RNA vaccines are all being researched and developed. Clinical trials are being conducted for many cancers, including bladder cancer, brain tumors, breast cancer, cervical cancer, Hodgkin lymphoma, and leukemia. Related clinical trials will incorporate treatment in the adjuvant or neoadjuvant settings and will involve patients with more indolent metastatic disease, in order to learn more and overcome some limitations of cancer vaccines.
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Salvatore Volpe, MD, FAAP, FACP, CHCQM
Chief Medical Officer