Abstract
We present a case of a patient with recurrent prostate cancer after treatment for favorable intermediate risk cancer. There was an exceptionally steep increase in PSA from <0.5 to 130ng/mL in 27 months accompanied with the development of bone metastasis. The PSA increase was unexpected. We suspect that this unusual development of metastases must have been caused by an impairment of the immune system caused by his IgG4 disease, and this may have allowed residual prostate cancer cells in the prostate to spread quickly. The influence of IgG4 on cancer is debated.