Table 1 Inclusion and exclusion criteria

Inclusion criteria:

• Having received curatively intended treatment for any malignant neoplasm;

• Primary treatment (surgery, radiotherapy, chemotherapy) being completed ≥3 months ago before study inclusion. Any other ongoing anti-tumor therapy is allowed (e.g., hormonal therapy, adjuvant immunotherapy);

• Bodily disturbances (BIS ≥10) (= clinical cutoff for body image dissatisfaction [9]); OR ((BIS = 2–9) AND ((patient-assessed distress due to bodily changes (VAS-B; 0–10) ≥ 5) OR (therapist-assessed awareness of bodily changes (VAS-A) ≥ 5 AND therapist-assessed related distress due to bodily changes (VAS-B, 0–10) ≥ 5)))

• No sign of progress or recurrence of malignancy at study inclusion according to treating physician;

• Score of 0 or 1 according to the PS of the ECOG [41];

• Having an anticipated life expectancy of ≥12 months, according to treating physician (recent evidence suggests that this is the best source for prediction of survival [42]);

• Age 18 years or older;

• Capacity to participate in group BPT sessions in Basel or Winterthur, 3 study assessments, and the smartphone-triggered interventions;

• Ability to provide informed consent.

Exclusion criteria:

• Suffering from a severe current mental disorder;

• Risk of current suicidality, as indicated by a suicide item score ≥ 2 in the BDI-II [43], as this group BPT intervention is not appropriate to support suicidal patients in acute crises. (Given a score ≥ 2, need for support will be assessed and if required, patients are instructed to call for or transferred to local psychiatric support);

• Participation in any other clinical trial with a psychosocial intervention;

• Receiving any other current psychotherapeutic treatment with the exception of already existing long-lasting therapies (≥ 6 months);

• Inability to understand and speak German.