2086 - Role of SBRT in the Management of Metastatic Colorectal Cancer: Oncologic Outcomes and Prognostic Factors from a Single-Institution Experience

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 17

POSTER

Presenter(s)

Firas Almomen, MBBS - King Saud University Medical City, Riyadh, Riyadh

K. K. Hassan^1,2, F. A. Almomen¹, B. A. Alruhaimi¹, N. Almazrou¹, M. Alalshaykh³, and A. A. Alsuhaibani¹; ¹Oncology Center, King Saud University Medical City, Riyadh, Saudi Arabia, ²Kasr Al-Ainy Center of Clinical Oncology (NEMROCK), Cairo University, Cairo, Egypt, ³Security Forces Hospital, Riyadh, Saudi Arabia

Purpose/Objective(s):

In the context of limited prospective evidence, we aimed to assess the benefit of stereotactic body radiotherapy (SBRT) as metastasis-directed therapy (MDT) in the management of metastatic colorectal cancer (mCRC) patients treated at our institution.

Materials/Methods:

This retrospective study included a cohort of 58 mCRC patients, diagnosed between 2016 and 2023, and managed per GI tumor board recommendations. Patients were evaluated according to baseline clinicopathological characteristics, tumor burden, metastatic status at the time of SBRT per EORTC classification (de-novo, repeated & induced oligo-metastases), and treatment-related factors.

The primary endpoints were local control (LC) & overall response rate (ORR). Secondary endpoints included time to progression (TTP) & overall survival (OS). Survival outcomes were analyzed using Kaplan–Meier methods, and prognostic factors were assessed using Cox proportional hazards models.

Results:

At a median follow-up of 66 months, the median age was 61 years at diagnosis. Synchronous metastases were present in 62% of patients. 59% of primary tumors originated in the rectum versus 41% in the colon, with 93% of cases having their primary resected. Poorly differentiated tumors and mucinous histology subtypes were identified in 9% and 15%. KRAS and BRAF mutations were detected in 53% & 4% of cases, respectively, while 98% had low microsatellite instability (MSI L).

At baseline, 74% of the patients were oligometastatic (=5 lesions). A total of 174 lesions were treated over 96 SBRT courses, with 45% of patients receiving two or more courses. A biologically effective dose (BED10) =100 Gray (range 60-151) was delivered in 76% of treatments. The lung was the most frequently treated site (52%), followed by the liver (33%) & lymph nodes (24%).

The ORR was 88%, with complete remission achieved in 52%. The 1- and 2-year (LC) rates were 79% and 72%, respectively. Improved LC was significantly correlated with BED10 >100 Gray (P=0.0003), tumor size <2 cm (P=0.004), and number of lesions treated per course (P=0.001).

The median (TTP) following SBRT was 5.3 months; however, it significantly reached 20.3 months for de novo treated lesions (P=0.0006). While lung-directed SBRT (P=0.003) and initially poly-metastatic disease (P=0.03) were significantly associated with inferior TTP. Notably, 57% of patients were still oligometastatic when progressed, and 14% remained progression-free.

The median (OS) was 54 months. Elevated CEA level (>5) was significantly associated with inferior OS (P=0.007), whereas improved OS was observed in patients who received a second SBRT course (P=0.04) or third-line systemic therapy (P=0.005). While 48% of patients underwent metastasectomy, this was linked to a non-significant trend toward better OS. Finally, no grade =3 toxicities were reported.

Conclusion:

Our results support SBRT as a non-invasive, effective, and practical MDT option in mCRC patients, offering durable LC and favorable OS, with curative potential.