ESTRO 2024 - Abstract Book

S1993

Clinical - Mixed sites, palliation

ESTRO 2024

incidence and predictive factors of lymphopenia in patients with advanced and refractory solid tumors treated with stereotactic body radiation therapy (SBRT) combined with an immune checkpoint inhibitor.

Material/Methods:

Clinical, biologic and dosimetric data of patients previously enrolled in an international phase II trial (SABR-PDL1, NCT02992912) that investigated the safety and preliminary efficacy of the anti-PDL1 atezolizumab combined with three-fraction SBRT delivered concomitantly with the second cycle of immunotherapy. Analyzed patients had metastatic colorectal cancer (CRC), non-small cell lung cancer (NSCLC), renal cell cancer (RCC) or sarcoma and received SBRT to at least one tumor localization selected by the physician. The incidence of severe lymphopenia (defined as grade III-IV, <500mm 3 , according to the CTCAE criteria) at the time of nadir was studied. The dosimetric and clinico-biologic predictors of lymphopenia were evaluated by logistic regression models. Overall and progression-free survival (OS, PFS) were plotted with Kaplan Meier curves and analyzed with logrank tests.

Results:

Ninety metastatic patients with 97 irradiated lesions were included in the analysis. Thirty (33%) had CRC, 48 (53%) had sarcoma, seven (8%) had NSCLC, and five (6%) had RCC. Eighty-one (90%) patients had prior oncologic surgery, 53 (59%) had prior radiotherapy, and 38 (42%) had three or more lines of systemic treatment. All patients were treated with three fractions of SBRT. Eighty-three patients (92%) had only one lesion irradiated. The median prescribed dose was 38.25 Gy (range 21-45 Gy). The most commonly irradiated sites were the lung (51%), followed by the liver (23%). Twenty-three patients (25%) developed severe lymphopenia. Characteristics were similar among patients with and without severe lymphopenia, except for history of previous irradiation (78 versus 52%, p=0.047). Univariable analysis showed that the primary tumor site (odds ratio (OR) 3.29, 95%CI[1.15 - 9.38], p=0.02), prior radiotherapy (OR 3.29, 95%CI[1.09-9.89], p=0.03), and pretreatment lymphocyte count (OR 0.03, 95%CI[0.01-0.15]), p<0.001) were significant predictors of severe lymphopenia. Pretreatment lymphocyte count was the only significant predictor of severe lymphopenia in multivariable analysis (OR 0.04, 95%CI[0.01-0.17], p<0.001) (Table 1). Patients with severe lymphopenia had decreased OS versus those without, 18.8 (range 12.3 - 38) versus 43 (range 28.0-56.5) months, respectively, p=0.047 (Figure 1). PFS of patients with severe lymphopenia was 4.7 months (range 1.6-10.7) versus 4.9 months (range 4.7-8.1) for those without, p=0.44.

Table 1. Logistic regression analysis on predictors of severe lymphopenia.

Univariable

Multivariable

Variable

Odds Ratio (95% CI) 0.9996 (0.9631,1.0376)

P value

Odds Ratio (95% CI)

P value

Age Sex

0.99 0.47

1.42 (0.54,3.73) 3.29 (1.15,9.38) 0.89 (0.26, 3.02) 1.2 (0.92,1.57)

Primary tumor

0.02*

1.14 (0.27,4.74)

0.86

RT site

0.85

Prior lines of systemic treatment

0.175

Prior RT

3.29 (1.09,9.89)

0.03*

1.29 (0.29,5.65)

0.74

PTV volume

0.9998 (0.9954,1.0042)

0.91

Dose prescribed

0.98 (0.92,1.05) 0.98 (0.93,1.02) 0.03 (0.01,0.15)

0.6

PTV Dmax

0.32

Pretreatment ALC

< 0.001*

0.04 (0.01,0.17)

< 0.001*