Characteristics and outcomes for fecal occult blood test (FOBT) screen detected (SD) versus non-screen detected (NSD) colorectal cancer (CRC).

Abstract

42 Background: FOBT based screening for CRC has been shown in multiple studies to reduce CRC mortality. Beyond the well described earlier stage at diagnosis, other characteristics of SD cancers have not been well studied. Since 2006 Australians aged 50-74 have regularly been mailed an immunochemical FOBT via the National Bowel Cancer Screening Program (NBCSP), with participation rate stable around 40%. Methods: To explore patient (pt), tumour, treatment and outcome data for SD compared to NSD, we examined a multi-site CRC database where prospectively collected data includes method of detection. Categories include SD via the NBCSP, cases that were symptomatic or incidentally found on imaging (NSD), and cases detected by screening outside the NBCSP (OSD). High risk features for Australian Clinicopathological Staging System (ACPS) Stage B included emergency presentation, T4, lymphovascular invasion and <12 lymph nodes examined. Results: Of 6969 registry pts diagnosed 06/2006–06/2020, 4107 (59%) were aged 50-74, including 473 (12%) SD, 3228 (79%) NSD and 406 (10%) OSD. SD versus NSD pts were younger (mean 62.4 v 64.2 years), had better ASA score (ASA 1-2: 79% v 66%, Odds Ratio [OR] 1.9, p<0.001), earlier stage at diagnosis (ACPS A/B/C/D = 38%/21%/28%/5% v 17%/29%/26%/21%, p<0.001), were more often left-sided (41% v 33%, OR 1.44, p<0.001) but less frequently located in the rectum (28% v 36% OR 0.70, p=0.001). There was no difference by gender. SD tumors were more often well/moderately differentiated (76% v 66%, OR 1.65, p<0.001) and less often mucinous (16% v 20%, OR 0.66, p=0.002). SD stage A tumours were more often T1 (66% v 43%, OR 0.36, p<0.001). SD stage B tumours were more often T3 (92% v 85%, OR 0.43, p=0.033), and had fewer high risk features (60% v 49%, OR 0.64, p=0.036). SD stage C pts had a similar rate of N2 disease (25% v 31%, p=0.20), but more often received adjuvant chemotherapy (96% v 86%, OR 3.6, p=0.002). De novo stage D and relapsed SD pts more often underwent metastatic resection (46% v 25%, OR 2.6, p<0.001). Relapse free survival (RFS) in stage A-C, progression free survival in stage D (PFS), and overall survival (OS) was superior for SD and is in Table. Conclusions: We show for the first time to our knowledge that SD CRCs have many distinct and favourable prognostic features that appear to be driving favourable stage based outcomes when compared to NSD patients. This prognostic data could inform adjuvant therapy decision making and surveillance strategies for SD CRC. [Table: see text]