OBJECTIVES: This study evaluated treatment patterns and duration of treatment (DOT) for patients with MSS mCRC in the USA. Treatment patterns and DOT have not been assessed in this population and are needed to support pioneering of novel treatment combinations.

METHODS: A retrospective observational study using the Flatiron Health electronic medical records database was conducted among patients with MSS mCRC who received first-line (1L) therapy on or after January 1, 2013. Descriptive statistics were used for treatment frequencies, treatment sequences, and DOT. DOT was defined as the time between start and end dates for therapy.

RESULTS: This study identified 7636 patients with MSS mCRC and 1L treatment. Mean age was 62 years, 55% were male, 63% were white, 65% had stage IV disease at initial diagnosis, and 72% had an ECOG score of less than 2. Among patients tested for mutations, 45% had positive KRAS, 5% had positive NRAS, and 7% had positive BRAF. Fifty-six percent of patients subsequently received 2L treatment and 28% received 3L. The most common regimen was FOLFOX plus bevacizumab (34%) in 1L, FOLFIRI plus bevacizumab (26%) in 2L, and TAS-102 (14%) in 3L. The most common sequence for 1L to 2L was FOLFOX plus bevacizumab followed by FOLFIRI plus bevacizumab (22%) and for 1L to 3L was FOLFOX plus bevacizumab followed by FOLFIRI plus bevacizumab followed by TAS-102 (4%). Median DOT was 5.1 months (95% CI 5.10–5.29) in 1L, 3.7 months (95% CI 3.68–3.94) in 2L, and 3.0 months (95% CI 2.79–3.09) in 3L.

CONCLUSIONS: Patients with MSS mCRC predominately received bevacizumab plus chemotherapy in 1L and 2L, with a high proportion continuing bevacizumab through progression. There was no predominant regimen in 3L and median DOT was less than 3.0 months, which highlights the unmet need for more effective treatment options in 3L.