Interferons are chemicals that are part of your body’s normal immune system. There are several subtypes of interferons, including α-interferon. BCG is, at least in part, effective against bladder cancer because it causes an increase of α-interferon in the bladder, which in turn helps to kill cancer cells. Interferon can be pre-pared and concentrated in a solution. Logically, by instilling it into the bladder, one could get a similar effect to BCG treatments with fewer side effects. Unfortunately, the effects of BCG appear more complex than just interferon.
When used alone, interferon initially performs about as well as BCG. Over time, however, patients treated with BCG have fewer recurrences, which indicates that the effect of BCG involves more than just activating interferon. The side effects of interferon are similar to those of BCG, meaning up to 27% of patients experience fever, chills, fatigue, and muscle aches (similar to having a mild flu).
Combining interferon with BCG is the most common way in which it is used today. Patients who have received BCG in the past but now have recurrences are often treated with combined interferon/BCG. Also, patients who have been unable to tolerate full-dose BCG can be treated with low-dose BCG combined with interferon with good effect.