Secondary hypotheses: Compared to the control group (SPC), patients receiving ACT-group therapy will at eight and twelve months after baseline: 1. Report statistically and clinically significant reductions in somatic symptoms. 2. Report statistically and clinically significant lower symptom interference and at twelve months after baseline: 3. Show significant improvement in alterations of stress response and inflammatory response. The patients receiving ACT-group therapy will show good feasibility regarding treatment.