One third of individuals aged >60 years will be diagnosed with at least one renal cyst following abdominal imaging. These cystic lesions are categorized according to the Bosniak classification which categorizes cysts according to their degree of complexity and risk of malignancy. Growing evidence suggests that a significant proportion of Bosniak III and IV cysts are benign and that the malignant ones present low metastatic potential. Since renal surgery carries substantial morbidity (20%) and potential mortality (0.5%), active surveillance has gained attention as a potential tradeoff to surgery to overcome overtreatment. Therefore, prospective studies of long-term follow-up are needed to confirm the oncologic safety of this strategy for patients with Bosniak III/IV cysts.

This is an multicenter prospective observational longitudinal study. The main objective is to compare the 5-year follow-up cancer-specific survival between the active surveillance and the surgical groups.

Background: One in three patients over 60 years old will be diagnosed with a renal cyst following abdominal imaging. Traditionally, experts have recommended that complex cystic lesions (also known as Bosniak III - IV cysts) should be surgically removed, but recent evidences suggest that many are benign or have low metastatic potential. Thus, active surveillance which involves close follow-up of a patient's condition, was proposed as a tradeoff option to surgery.

Design: Multicenter observational longitudinal prospective cohort study

Objectives: The goal of this multicenter project is to conduct a prospective study with a 5-year follow-up to confirm the oncologic outcomes of active surveillance in the management of complex cysts. The main objectives are: 1) to compare the 5-year cancer specific survival between cysts managed by surgery and active surveillance; 2) to evaluate disease progression; 3) to evaluate patient's well-being according to each management strategy; and 4) to compare the 5-year healthcare cost of both management approaches.

Study population: Patients incidentally diagnosed with a Bosniak III and/or IV cysts, who are deemed to have at least 5 years of life, and who opted to be managed by either surgery or active surveillance. (N=330)

Follow-up: Patients will DECIDE if they want to have a surgery or to be followed by active surveillance. All patients will be followed as per standard of care with either semi-annual and annual visits. Research visits will serve to assess vital status and quality of life scores (through validated questionnaires). Patients on active surveillance will also be assessed for cyst progression and might be offered invasive or systemic therapy if progression is observed.

Inclusion Criteria:

• 18 years old and older;
• diagnosed with a Bosniak III or IV cyst (classification 2019);
• size of cystic component ≤7cm;
• cyst wall/septum nodule (obtuse margin of protrusion) <10mm (perpendicular axis) or nodular/solid component ≤2 cm in any axis;
• life expectancy >5 years (by physician's estimate);
• new diagnosis ≤ 12 months from accrual date;
• currently asymptomatic from the disease;
• deemed fit enough for surgery;
• willingness and ability to complete questionnaires in either French or English;
• able and willing to provide informed consent

Exclusion Criteria:

• history of a hereditary renal cancer syndrome;
• presence of polycystic kidney disease;
• any prior history of RCC;
• received systemic therapy for another malignancy within the 12 months prior to accrual;
• uncontrolled medical illness including infections, hypertension, arrhythmias, heart failure, or myocardial infarction/unstable angina within 6 months that would predispose to immediate surgical therapy;
• metastatic disease or evidence of vascular or nodal disease;
• unwillingness to undergo monitoring and imaging studies;
• any contra-indication(s) to contrast-enhanced imaging (estimated glomerular filtration rate <30min/mL)

Patients incidentally diagnosed with a Bosniak III or IV cysts and who opted to be managed by either surgery or active surveillance