Early low blood MALT1 expression levels forecast better efficacy of PD‑1 inhibitor‑based treatment in patients with metastatic colorectal cancer.

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) modulates colorectal cancer (CRC) malignant behaviors and tumor immune escape. The present study aimed to explore the association of MALT1 with treatment response and survival time among patients with metastatic CRC (mCRC) after programmed cell death protein-1 (PD-1) inhibitor-based treatment. MALT1 from the blood samples of 75 patients with unresectable mCRC receiving PD-1 inhibitor-based treatment at baseline and after 2-cycle treatment, as well as 20 healthy controls (HCs), was detected by reverse transcription-quantitative PCR. In the patients with mCRC, the objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS) and overall survival (OS) were calculated. MALT1 expression was elevated in patients with mCRC compared with that in HCs (P<0.001). In patients with mCRC, MALT1 expression was positively correlated with multiple (vs. single) metastasis (P=0.032) and peritoneum metastasis (P=0.029). MALT1 levels before treatment were decreased in ORR patients vs. non-ORR patients (P=0.043) and in DCR patients vs. non-DCR patients (P=0.007). Additionally, MALT1 expression was reduced after treatment compared with that before treatment (P<0.001). Meanwhile, MALT1 expression after treatment was notably decreased in ORR patients vs. non-ORR patients (P<0.001) and in DCR patients vs. non-DCR patients (P<0.001). Furthermore, a low MALT1 level before treatment was associated with longer PFS (P=0.030) and OS (P=0.025) times. Decreased MALT1 expression after treatment and a decline in MALT1 expression of >30% after treatment (ratio to MALT1 before treatment) (both P≤0.001) presented more significant associations with prolonged PFS and OS times. In conclusion, early low levels of blood MALT1 during therapy may predict an improved response to PD-1 inhibitor-based treatment and survival time in patients with mCRC.