Hepatocellular carcinoma (HCC) is the most common gastrointestinal neoplasm with high mortality [1], only behind lung and colorectal cancers. The incidence of HCC is increasing in some populations and has become a major public concern. The main risk factors for the development of HCC in China are viral hepatitis and excessive alcohol consumption. Among these, hepatitis B virus (HBV) and hepatitis C virus (HCV) are the most important risk factors for HCC [2]. Recently, HCC has been considered a metabolic disease owing to progress in metabolic analysis [3]. As for its treatment, only a small proportion of HCC patients are diagnosed with early tumor-node-metastasis (TNM) stage, where surgical resection or liver transplantation can be performed [4]. However, most patients with HCC present with advanced TNM stages, with palliative care being the only remaining option. Malignant ascites is the most common clinical sign of advanced HCC. The most common type of malignant ascites in HCC is characterized by a high volume, persistence, and recurrence. At the same time, little is known about the relationship between microbial and malignant tumors within ascites.

Malignant ascites is a common manifestation of terminal events in some gastrointestinal cancers, including HCC [5], and it is a sign of deterioration in the quality of life and a poor survival outcome [6]. Commonly used methods for the clinical management of malignant ascites include diuresis, ascites drainage, laparotomy, chemotherapy, targeted therapy, and immunotherapy [7]. These therapies only relieve some symptoms, do not address the underlying problem, and cause many side effects. Due to the complex composition of cellular and microbial components, malignant ascites generates a unique tumor microenvironment that mediates the metastasis of cancer cells [8]. Hence, gaining a deep insight into the pathogenesis of malignant ascites is critical for conquering the disease.

With the rapid progression of sequencing technologies, a close relationship between gut microbes, cancer occurrence, and metastasis has been revealed [9]. The role of the microbiology in the development and progression of HCC has been reported in many researches [10], [11], [12], but the role of the intratumoral microbiome in the progression of malignant ascites secondary to HCC remains unknown. Gustave Roussy Immune (GRIm) is a novel immune and inflammatory index which has been reported to be correlated with survival outxomes of several cancers. A real-word study conducted by Jian et al. [13] concluded that GRIm score is a reliable prognostic biomarker in individuals with lung cancer receiving immunotherapy. Another clinical trial demonstrated that the changes of GRIm score after two courses of nivolumab therapy compared to pretreatment values proved beneficial in predicting nivolumab sensitivity [14]. Besides, GRIm-Score is an independent prognostic indicator of overall survival of first-line chemotherapy for patients with lung adenocarcinoma [15]. Hence, GRIm-Score is not only a selection marker for immunotherapy, but also a promising pretreatment prognostic biomaker for chemotherapy among cancer population.

This study has attempted to compare the prognostic significance of serum GRIm (sGRIm) and ascites GRIm (aGRIm) scores in patients with malignant ascites secondary to HCC. We also sought to explore the association between the GRIm-score and intratumoral microbial alterations in patients with malignant ascites secondary to HCC. Finally, we investigated the correlation between the GRIm-score levels and immune cells in malignant ascites. This study has aimed to elucidate the interplay between intratumoral microbiome and immune cells in malignant ascites secondary to HCC.