Stage distribution utilizing magnetic resonance imaging in an unselected population of primary rectal cancers

Pre-operative radiotherapy (RT) or chemo-radiotherapy (CRT) are sometimes recommended prior to rectal cancer surgery, but guideline recommendations vary. The aim was to describe stage distribution and other important characteristics required for the treatment decision of patients with primary rectal cancers utilizing magnetic resonance imaging (MRI) in an unselected population.

All 796 histopathologically verified rectal adenocarcinomas diagnosed 2010-2015 in two counties in Sweden (population 630,000 in 2015) were identified. Staging with pelvic MRI unless contraindications were present, treatment and pathology followed Swedish guidelines.

Twenty-three % of cases (n = 186) had distant metastases at diagnosis, demonstrating more advanced tumor and nodal stages when compared with non-metastatic patients (p < 0.001), and they more often displayed MRI-identified mucinous features and extramural vascular invasion (EMVI) than non-metastatic tumors (p < 0.001 for both). In non-metastatic patients, 8% displayed clinical stage T1 (cT1), 21% cT2, and 53% cT3; one-third of the latter threatened or involved the mesorectal fascia (MRF+). Almost 20% had stage cT4 (4% cT4a, 14% cT4b) of which 50% were considered "non-resectable". EMVI was seen in 33% of cT3M0 tumors and in 48% of cT4M0 tumors.

In an unselected population, approximately 80% of primary rectal cancers are referred to as "locally advanced" (stage II-III, or cT3-4 or N+), meaning that they, according to many international guidelines, are recommended neo-adjuvant treatment. This study provides a detailed description of the clinical stages and presence of characteristics identifiable on MRI which are of importance when assessing the needs for RT/CRT, when using different guidelines.