Do cancer vaccines work?
There have been a number of clinical studies that have tested cancer vaccines. Thus far, no trials have found that cancer vaccines improve overall survival. However, a number of important findings have come out of these studies:
- Cancer vaccines are well-tolerated 3-5
A number of Phase I and II trials have shown that cancer vaccines are generally well-tolerated, particularly with the viral and peptide vaccines. Phase I trials have reported very few significant toxicities with these vaccines. The most common toxicity in all of these trials has been local irritation at the site of the injection. In fact, it appears that patients that have a stronger local reaction to the injection may have a better response of the tumor to the treatment. This may be because a local reaction serves as a marker for people who have a good immune response to the vaccine. Patients with strong local reactions will likely have a strong reaction to the tumor as well.
- Cancer vaccines induce an immune response 6-9
In both Phase I and Phase II trials, levels of immune activity have been measured in patients receiving cancer vaccines. Routinely, objective measures have shown an increase in the immune activity in a number of patients receiving cancer vaccines. In addition, patients who have a good immune response by objective measures have a better response of their tumors to the vaccine.
- Several cancer vaccines show a good tumor response compared to historical results
Recently, the results of a non-randomized trial utilizing a melanoma vaccine were reported. 10 Patients receiving the vaccine had a 5-year overall survival of 44%. Given the advanced disease in these patients, these results were quite good, and noticeably higher than historical surgical series of patients with similarly advanced disease showing 5-year overall survival rates of 20-25%. Another promising trial was recently reported which used a prostate cancer vaccine in patients with progressive disease (judged by rising PSA levels) after local therapy for prostate cancer. 11 After a year and a half, 45% of patients did not have further increases in their PSA.
- Results of Phase III, randomized trials have been disappointing
Despite the promising results in earlier trials, several large randomized trials have failed to show an overall survival advantage with the use of vaccines. 12 A large trial by the Southwest Oncology Group for patients with melanoma who did not have spread of their disease to the lymph nodes showed no improvement in overall survival for patients who received the vaccine following surgery compared to patients who underwent surgery alone. 13 Another trial for patients with renal cell carcinoma showed a small decrease in the percentage of patients who had progression of their cancer with the addition of a cancer vaccine. 14 Again, however, there was no improvement in overall survival with the use of the vaccine.