Stool and symptom testing in ColoREctal Evaluation for Neoplasia in Cystic Fibrosis (SCREEN-CF).

Background: People with cystic fibrosis (pwCF) have increased colorectal cancer (CRC) risk. Colonoscopy is recommended, yet CF comorbidities increase complexity and risk.

Methods: We conducted a prospective, observational study of pwCF meeting colonoscopy screening guidelines at an Australian centre (2019 - 2023). Immunochemical faecal occult blood test (iFOBT), faecal calprotectin (FC), and faecal tumour pyruvate kinase isoenzyme type M2 (TuM2-PK) were evaluated for detecting adenomatous polyps and malignant ileocolonic lesions in pwCF. Stools were collected within 3 months of colonoscopy. Diagnostic performance and optimal cut-offs were calculated.

Results: Among 49 participants [mean (SD) age 47.8 (8.2) years; 53 % female], 12 (24.5 %) were post-solid organ transplant, 10 (20.4 %) had > 3 months of triple modulator therapy at stool testing, 12 (24.5 %) had adenomatous polyps and 2 (4 %) had ileocolonic malignancy. Malignancies were in non-transplanted individuals, in the terminal ileum (age 43) and hepatic flexure/ascending colon (age 48). Higher BMI (>23.5 kg/m²) was associated with abnormal colonoscopy (p = 0.03). iFOBT, FC and TuM2PK demonstrated excellent predictive performance for malignancy (AUC 0.93, 1.00, 0.83; all p < 0.05). Only FC had acceptable predictive performance for pre-malignant lesions (AUC 0.73; p = 0.008). For adenomatous polyps, FC ≤100 µg/g achieved a sensitivity of 91.7 % and an NPV of 95.5 %. For ileocolonic malignancy, FC ≥1000 µg/g showed 100 % sensitivity and specificity (p = 0.0009).

Conclusion: CRC screening in pwCF is critical given the high prevalence of neoplasia. Alternative non-invasive screening may support risk stratification among individuals with comorbidities, or reluctance, though performance could be influenced by CFTR modulator therapy.