Can cancer vaccines added to hormonal therapy improve survival?

This study examined whether a combination of hormonal therapy and therapeutic cancer vaccination is an effective treatment for patients with estrogen positive (ER+) metastatic breast cancer (cancer that has spread beyond the breast, to distant organs and tissues of the body).

Vaccines are used to prevent many diseases by activating an immune response to fight diseases. This immune response leads to the formation of antibodies, substances that find and kill the invading disease. Therapeutic cancer vaccines are being explored as a possible treatment for metastatic breast cancer (BC). Cancer cells are lined with proteins called mucins, which increase cancer growth. A substance found on mucin, sialyl-Tn (STn) also increases tumor growth and is associated with a worse prognosis in ER+ BC (cancer that depends on estrogen, the main female sex hormone, to grow). A synthetic STn is used in an anticancer vaccine called STn-KLH (Theratope). It is thought that by introducing more STn into the body through vaccination, the immune system will build antibodies against both the synthetic and natural STn, thus stopping tumor growth. Previous clinical trials have found the STn-KLH vaccine to be safe and well-tolerated by patients, but did not find a benefit regarding time to progression or TTP (the time it took for the BC to progress or grow) or overall survival (OS). This study aimed to evaluate whether adding the vaccine to hormonal therapies could benefit patients with ER+ metastatic BC in terms of TTP and OS. 

The records of 350 patients with metastatic BC who underwent hormone therapy while participating in a previous STn-KLH clinical trial were examined. 180 of these patients received the STn-KLH vaccine, while the remaining 170 received a placebo vaccine (a substance with no effect on the body used as a comparison).

Results showed that OS was higher in patients given the STn-KLH vaccine in addition to hormonal therapy as compared to the control group. Patients who had a stronger immune response following the vaccination (measured by the level of antibodies produced) had a significantly longer average OS (39.6 months) than patients who had a weaker immune response (25.4 months). Patients with stronger immune responses also tended to have a longer TTP (10.5 months) compared to patients with a weaker immune response (6.3 months), but this difference was not statistically significant. 

In summary, the addition of the STn-KLH vaccine to hormonal therapy increases survival time and delays cancer progression in women with metastatic ER+ breast cancer.

This research was funded by Biomira, Inc. and Merck KGaA, the manufacturers of Theratope. 

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