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Metastasis, a main cause of death in tumor patients, is a complicated process that involves multiple steps, presenting a major clinical challenge. Tumor cells break the physical boundaries of a primary tumor, intravasate into the lumina of blood vessels, travel around through blood circulation, extravasate into distant organs, colonize the host organs, and eventually develop into the foci of metastatic cancer. The metastasis of tumor cells exhibits organ-tropism, i.e., tumor cells preferentially spread to specific organs. Liver is a common site for metastasis. The pattern of metastasis in uveal melanoma, colorectal carcinoma, and pancreatic ductal adenocarcinoma shows organ-tropism for liver. The anatomical structure of liver determines its hemodynamic characteristics, e.g., low pressure and slow blood flow, which tend to facilitate the stasis and colonization of tumor cells in the liver. Besides the hemodynamic features, the metastatic colonization of liver depends largely on the interaction between tumor cells and the hepatic microenvironment (especially liver-resident cellular components). Resident cells of the hepatic microenvironment include hepatocytes, liver sinusoidal endothelial cells (LSECs), hepatic stellate cells (HSCs), Kupffer cells (KCs), etc. Herein, we discussed the role and significance of liver-resident cells in the metastatic colonization of tumor in the liver., (Copyright© by Editorial Board of Journal of Sichuan University (Medical Sciences).)

Lung adenocarcinoma (LUAD) is the most common subtype of lung cancer and one of the main causes of cancer-related deaths. In the past decade, with the widespread use of computed tomography (CT) in routine screening for lung cancer, the incidence of LUAD presenting as small pulmonary nodules radiologically, has increased remarkably. The mechanisms of the occurrence and progression of LUADs are complex, and the prognoses of patients with LUAD vary significantly. Although significant progress has been made in targeted therapy and immunotherapy for LUADs in recent years, the drug resistance of tumor cells has not been effectively overcome, which limits the benefits of patients. With the accomplishment of the Human Genome Project, sequencing-based genomic and transcriptomics have come into the field of clinical and scientific researches. Single-cell sequencing, as a new type of sequencing method that has captured increasing attention recently, can perform specific analysis of cell populations at single-cell level, which can reveal the unique changes of each cell type. Single-cell sequencing can also provide accurate assessment on heterogeneous stromal cells and cancer cells, which is helpful to reveal the complexity of molecular compositions and differences between non- and malignant tissues. To sum up, it is an urgent need for clinicians and basic scientists to deeply understand the pathogenesis and development of LUAD, the heterogeneity of tumor microenvironment (TME) and the mechanism of drug resistance formation through single-cell sequencing, so as to discover new therapeutic targets. In this paper, we reviewed and summarized the application and progress in single-cell sequencing of LUADs.
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Colorectal cancer is one of the most common malignant tumors of digestive tract. There are a large number of microorganisms in the digestive tract. Under normal physiological conditions, intestinal microorganisms can help with digestion and absorption, resist pathogen invasion and regulate the proliferation of intestinal mucosal cells. However, intestinal microflora imbalance will affect the intestinal microenvironment and intestinal cell function, and is closely related to the incidence and progression of colorectal cancer. Firstly, this paper introduces the changes of intestinal flora in patients with colorectal cancer, and then summarizes the mode of intestinal flora participating in the occurrence of colorectal cancer from the macro level. Then, we elaborate the involvement of intestinal flora in colorectal cancer from the aspects of cytokine-dependent chronic inflammation, DNA damage of intestinal epithelial cells, carcinogenic metabolites of intestinal flora and cellular enzymes, and changes of intestinal immune system. The pathogenesis of colorectal cancer provides a reference for further study of the pathogenesis of colorectal cancer. Finally, from the perspective of intestinal flora and colorectal cancer treatment, we analyze the significance of probiotics and bacterial flora transplantation for the treatment of colorectal cancer, and provide some new treatment ideas and methods that may be useful for the treatment of colorectal cancer.

Objective: To analyze the clinicopathological features of type 2 diabetes mellitus complicated with colorectal cancer (DCRC). Methods: A case-control study was conducted. Inclusion criteria: (1) hospitalized patients receiving fibrocolonoscopy; (2) adenocarcinoma and mucinous adenocarcinoma diagnosed by pathology; (3) with preoperative cTNM clinical staging; (4) colorectal cancer patients undergoing surgical treatment; (5) with postoperative pTNM staging; (6) no smoking or drinking habits. Exclusion criteria: (1) familial adenomatous polyposis (FAP); (2) Lynch syndrome; (3) carcinoma of anal canal and perianal carcinoma; (4) multiple primary cancer; (5) with serious cardiocerebrovascular diseases or multiple organ failure. Clinicopathlogical data of 32 DCRC patients who were diagnosed and treated in Peking University Shougang Hospital from December 2017 to December 2018 were retrospectively collected and analyzed. Forty nondiabetic colorectal cancer (CRC) patients during the same period were selected as control group according to the sex ratio and the age difference less than 5 years. Student's t test and χ(2) test were used to compare the difference between the two groups in baseline clinicopathological data, clinical test results, tumor markers and infiltration status of T cells in tumor immune microenvironment. Results: Among 32 DCRC patients, 24 were males and 8 were females with a mean age of (63.0±1.7) years; among 40 CRC patients, 30 were males and 10 were females with a mean age of (60.5±1.6) years. The duration of diabetes mellitus in DCRC patients (from the diagnosis of diabetes mellitus to the diagnosis of colorectal cancer) was (9.2±1.3) years. The body mass index (BMI) of DCRC group was significantly higher than that of CRC group [(24.8±0.6) kg/m(2) vs. (23.2±0.4) kg/m(2), t =2.372, P= 0.020]. There were no significant differences in other baseline data (sex, age, primary site of tumor, R0 resection rate, pathological stage, pathological type, differentiation degree of tumor, preoperative intestinal obstruction) between the two groups (all P >0.05). Serum triglyceride level in DCRC group was higher than that in CRC group [(2.1±0.2) mmol/L vs. (1.5±0.1) mmol/L, t= 3.085, P =0.003], while hemoglobin [(120.3±5.2) g/L vs. (132.7±2.8) g/L, t =-2.224, P =0.029], anti- thrombin III [(94.2±3.7)% vs. (103.5±2.4)%, t =-2.197, P =0.031], and red blood cell count [(4.2±0.1)×10(12)/L vs. (4.5±0.1)×10(12)L, t =-2.055, P =0.044] were all lower than those in CRC group. The preoperative carcinoembryonic antigen (CEA) level in DCRC group was higher than that in CRC group [(50.3±21.8) μg/L vs. (5.6±1.0) μg/L, t =2.339, P =0.022]. There were no significant differences in preoperative levels of other four tumor molecular markers (CA199, CA242, CA724 and CA125) between the two groups (all P >0.05). The expression of Foxp3 [specific markers of CD4+, CD25+ regulatory T cells (Treg)] in DCRC group was higher than that in CRC group [(82.7±6.2) cell/HPF vs. (62.6±4.9) cell/HPF, t =2.586, P =0.012]. There were no significant differences in the infiltration of CD4, CD8, PD-1 and PD-L1 positive cells between two groups (all P >0.05). Conclusions: The average diabetic history of DCRC patients is nearly 10 years. They have higher BMI and serum CEA level, and more Treg cell infiltration in the tumor. Close attention should be paid to these patients in clinical practice.

Objective: To investigate whether cancer-associated- fibroblasts (CAF), the key component of tumor microenvironment, regulate the chemoresistant capacity of lung cancer cell line A549 through SDF-1 secretion. Methods: Primary cell isolation techniques was used to isolate cancer-associated-fibroblasts from lung cancer patients. MTT assay was applied to determine the proliferation and chemoresistance of A549 cells. Quantative PCR was used to detect the mRNA changes of Bcl-xL. Western blotting was used to detect the protein expression of Bcl-xL. ELISA was applied to detect the SDF-1 secretion from normal fibroblasts (NF) and CAF. Results: CAF promoted the proliferation of A549 cells, while NF had no significant effect on them. After 72 hrs incubation, the absorbance value of A549+ CAF medium group was 0.814±0.006, significantly different from the 0.753±0.006 of the A549+ NF medium group ( P <0.05). The Q-PCR assay indicated that mRNA expressions of Bcl-xL in the A549 group, A549+ NF medium group and A549+ CAF medium group were 1.00±0.11, 1.10±0.09 and 3.50±0.30, respectively, showing a significant difference between the A549+ NF medium group and A549+ CAF medium group ( P <0.05). The Western blot showed that protein expressions of Bcl-xL in the A549 group, A549+ NF medium group and A549+ CAF medium group were 1.00±0.08, 1.10±0.12 and 3.10±0.25, respectively, with a significant difference between the A549+ NF medium group and A549+ CAF medium group ( P <0.05). The ELISA results showed that the SDF-1 concentrations in the A549+ NF medium group and A549+ CAF medium group were 3.23±0.02 and 9.53±0.10, respectively, significantly different from each other ( P <0.05). The MTT assay indicated that the absorbance values of OD of A549 group, A549+ AMD3100 group, A549+ NF medium group, A549+ NF medium+ AMD3100 group, A549+ CAF medium and A549+ CA Fmedium+ AMD3100 group were 0.43±0.03, 0.25±0.02, 0.48±0.03, 0.31±0.03, 0.72±0.06 and 0.45±0.03, respectively. The data of A549+ NF medium group was significantly different from that of A549+ CAF medium group ( P <0.05). Conclusions: Cancer-associated-fibroblasts enhance the drug resistance of A549 cells through SDF-1 secretion, upregulating the expression level of Bcl-xL through interaction with CXCR4. Our study not only illustrates that tumor microenvironment is able to enhance drug resistance of tumor, but also provides experimental evidence for the cancer-associated-fibroblasts as a potential therapeutic target for the treatment of lung cancer.

Drug efflux transporters plays a key role in pharmacokinetics parameters changes. In recent years, in addition to P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), MRP2 has become an advanced research hotspot. Several signaling pathways andtranscription factors have been reported to be involved in regulation of MRP2 expression in hypoxic microenvironment of tumor, such as peroxisome proliferators-activated receptors (PPARα), nuclear factor κB (NF-κB), pregnane X receptor (PXR), farnesoid X receptor (FXR), constitutive androstane receptor (CAR) and microRNA. But it is not fully understood how MRP2 is regulated under hypoxia. MRP2 is one of the most important efflux transporter proteins. Many drugs or inhibitors have been shown to be its substrate. In the hypoxic environment, changes in expression of MRP2 can significantly affect drug's pharmacokinetics (absorption, distribution, metabolism, excretion). Simultaneously, the regulation of MRP2 expression under hypoxic might involve several signal pathways and many genes, which constitute an integral gene regulatory networks.

Tumorigenesis is a complex process that is regulated by a variety of network signals. With the continuous development of the process, tumor cells gradually exhibit lots of hallmarks.Tumor cells have the characteristics of unlimited proliferation, resistance to apoptosis, evading immune surveillance, among others. As a unique organelles, mitochondria play an important role in cellular energy metabolism, reactive oxygen species producing and apoptosis process. Particularly, mitochondria have a close relationship with tumor development. In this review, we focus on the essential role of mitochondria in tumor cells development.

Tumor microenvironment has been confirmed to play an important role in the occurrence, invasion and metastasis of many kinds of tumors. Carcinoma-associated fibroblasts (CAFs) are the primary type of host cells in the tumor microenvironment. CAFs have an assignable role in tumor development. CAFs create a suitable "soil" for tumor origination, secrete a large amount of growth factors promoting tumor growth and angiogenic factors promoting tumor angiogenesis. In addition, CAFs attract a large number of inflammatory cytokines, and secrete a great quantity of soluble products promoting tumor cell invasion and metastasis. Therefore, CAFs may become new targets for targeted cancer therapy, and provide new ideas for the clinical cancer comprehensive treatment.