Most patients with non-medullary thyroid carcinoma (TC) achieve remission after primary treatment. Nonetheless, 30% develop recurrent disease and/or distant metastases resulting in worse survival. Patients with low- and intermediate-risk, whilst having a good prognosis, generally undergo similar primary treatment as those with a high-risk disease and face the risk of complications and burden of treatment, without a proven benefit in long-term outcome. For these patients, current guidelines state that less aggressive treatment (e.g. hemi-thyroidectomy vs. total thyroidectomy, and selective use of radioiodine (RAI) therapy), and tailored follow-up can be equally acceptable leaving room for patients' preferences. For high- risk patients, important unanswered question regard the optimal timing of starting tyrosine kinase inhibitors (TKI). For those who are asymptomatic or only mildly symptomatic, starting the treatment too early may expose them to side effects and impair quality of life, without evidence of a survival benefit.

Different patients have different views on these decisions, and so do physicians. Therefore, care should honour preferences and values of individual patients, and care should involve patients through shared decision making (SDM). The principle of SDM is twofold: 1. physicians provide patients with information on the existing options, and 2. help patients identify their preferences considering their individual values and needs. This involves important life values, for instance the desire to do everything possible, or to minimise complaints.

Addressing patients' treatment-related values is arguably the most difficult part of SDM so patient values are less likely to be discussed and honoured in a consultation. Current tools improve values deliberation but their effects are clearly insufficient. Tools should be integrated and applied in consultations to increase effectiveness. To strengthen values deliberation with TC as an example, a multifaceted intervention, COMBO, is proposed including 1) a patient values clarification exercise, named SDM-booster, 2) a physician values deliberation training using the SDM-booster, and 3) a patient decision aid. The SDM-booster strengthens values deliberation by 1) strengthening and clarifying patients' values and preferences, 2) communicating patients' values in the consultation, 3) serving as a focus in the values deliberation training.

Decision 1: total thyroidectomy vs. hemithyroidectomy:

Inclusion Criteria:

• patients with nodules >1 cm and <4 cm, with cytology result suspicious or malignant (Bethesda 5 or 6) with no clinical or radiological evidence of pathological lymph nodes and/or distant metastases before the primary (diagnostic) surgery
• patients with histologically (after diagnostic hemithyroidectomy) proven TC but are defined as low-risk according to the ATA classification.

Exclusion criteria:

• patients with multifocal TC
• patients with incomplete resection of the primary tumor
• patients with ATA defined intermediate risk or high risk

Decision 2: no treatment with RAI vs. treatment with RAI:

Inclusion criteria:

• patients with ATA defined low-risk and patients with multifocal papillary TC in the absence of other adverse features

Exclusion criteria:

• patients with ATA defined intermediate and high risk

Decision 3: active surveillance vs. systemic treatment

Inclusion criteria:

• patients with asymptomatic or mildly symptomatic RAI-refractory (slowly) progressive metastatic disease

Exclusion criteria:

• patients with coexisting conditions that do not allow prescription of TKI's

Other exclusion Criteria:

• lack of Dutch language proficiency
• mental incompetence hampering the process of shared decision making as judged by the physician