- Bile duct cancer is a type of tumor originating from epithelial cells, with late diagnosis and poor prognosis. Different sites (intrahepatic bile duct, hilar bile duct, extrahepatic bile duct) have their own specific diagnostic and therapeutic methods. Mixed hepatocellular cholangiocarcinoma is a specific subtype of primary hepatocellular carcinoma, and in clinical work, attention needs to be paid to intrahepatic cholangiocarcinoma caused by cirrhosis. Advanced cytological tests such as fluorescence in situ hybridization can help in the diagnosis of cholangiocarcinoma. Liver transplantation, although a treatment option for hilar cholangiocarcinoma, is not appropriate for both intrahepatic and extrahepatic cholangiocarcinoma. Clinicians and scientists worldwide are working to find the causative genes of cholangiocarcinoma, which will lead to new ideas for early diagnosis and individualized treatment of cholangiocarcinoma.
Background
Bile duct cancer is a group of malignant tumors that originate from epithelial cells and can be classified into the following types according to their anatomical sites: intrahepatic cholangiocarcinoma, hilar cholangiocarcinoma and extrahepatic cholangiocarcinoma.
Intrahepatic cholangiocarcinoma (ICC) refers to malignant tumors of epithelial cell origin in the bile ducts above the confluence of the left and right hepatic ducts. Its malignancy is high, its symptoms are insidious and its prognosis is poor. Because ICC is located in the liver, it resembles hepatocellular carcinoma (HCC) in some clinical aspects.
Most cholangiocarcinomas are highly, moderately, or poorly differentiated adenocarcinomas, with few other tissue types. Surgery is preferred for all types of cholangiocarcinoma, but it is important to consider whether the tumor invades blood vessels and lymph nodes. The highly pro-nodal hoof tissue proliferative capacity, rich tumor microenvironment and heterogeneity of cholangiocarcinoma determine its resistance to treatment.
Although surgery and liver transplantation can treat some patients with hilar cholangiocarcinoma, the 5-year survival rate is still very low. Gemcitabine + cisplatin combination chemotherapy regimens are usually used in patients who are inoperable. Local therapy may be used for intrahepatic cholangiocarcinoma, but there is insufficient conclusive evidence of efficacy.
A good understanding of the biological mechanisms of cholangiocarcinoma, the causative genes and the complex interactions between its tumor microenvironment may allow the selection of the best treatment option for patients and improve their survival. A systematic review of bile duct cancer is warranted given the recent interest in the research and treatment of bile duct cancer.
In this review, researchers focus on intrahepatic cholangiocarcinoma and hilar cholangiocarcinoma, as there have been many recent research developments in these two types.
Epidemiology and risk factors
Portohepatic bile duct cancer accounts for 50% of bile duct cancers, extrahepatic bile duct cancer accounts for 40%, and intrahepatic bile duct cancer accounts for less than 10%. According to WHO classification, mixed hepatocellular cholangiocarcinoma (also known as cholangiocarcinoma combined with hepatocellular carcinoma) is a recently recognized subtype of extrahepatic cholangiocarcinoma, accounting for less than 1% of all types of liver cancer.
Although intrahepatic cholangiocarcinoma is uncommon, its incidence appears to be on the rise in Western countries. The age-corrected incidence of cholangiocarcinoma is highest in Hispanic and Asian populations and lowest in non-Hispanic whites and blacks.
The incidence of the disease is higher in males than in females, except in the Hispanic female population, where the incidence of intrahepatic bile duct cancer is higher than in males; bile duct cancer is rare in children. Cumulative bile duct cancer mortality increased by 39% due to increased incidence, with higher mortality in men and boys than in women and girls.
Mortality from intrahepatic cholangiocarcinoma is highest among Indian American tribes and Alaska Natives and Asian populations, and lowest among whites and blacks. Increasing incidence and improved access to treatment have increased the incidence of cholangiocarcinoma.
Most bile duct cancers are primary and have no other risk factors. Some researchers have recently identified cirrhosis, hepatitis B and C as risk factors for cholangiocarcinoma (especially intrahepatic cholangiocarcinoma). Hepatitis C is common in Western countries and hepatitis B is common in Asia.
Studies from the United States and Europe found hepatitis C to be the most important risk factor for cholangiocarcinoma (especially intrahepatic cholangiocarcinoma), but studies from Korea and China found hepatitis B to be a risk factor for intrahepatic cholangiocarcinoma. A study from Japan confirmed the findings from Europe and the United States and concluded that hepatitis C was a more important risk factor for intrahepatic cholangiocarcinoma. All of the above studies confirm that cirrhosis is a risk factor for bile duct cancer.
In terms of pathogenesis, the release of inflammatory factors and cell death promote liver fibrosis while adding value to cells, but not all patients with bile duct cancer caused by viral hepatitis have cirrhosis in combination. A meta-analysis of risk factors for intrahepatic cholangiocarcinoma found a risk ratio of 22.92 for cirrhosis, 4.84 for hepatitis C, and 5.10 for hepatitis B.
Primary sclerosing cholangitis can progress to cholangiocarcinoma (especially hilar cholangiocarcinoma), which is characterized by chronic inflammation combined with liver injury and possible proliferation of progenitor cells, with a lifetime incidence of cholangiocarcinoma of 5-10% in these patients. Approximately 50% of patients with primary sclerosing cholangitis are diagnosed with cholangiocarcinoma within 24 months of diagnosis. The average age of diagnosis of cholangiocarcinoma in patients with primary sclerosing cholangitis is about 40 years, compared to about 70 years in the general population. Although there are many risk factors that can promote the development of primary sclerosing cholangitis to cholangiocarcinoma, these risk factors are not sufficient to guide disease surveillance in risk stratification.
Early diagnosis should also consider the presence of cystic bile duct disease, including Caroli’s disease, which has a lifetime incidence of bile duct cancer of 6%-30% in these patients with a median age of 32 years. The incidence of cholangiocarcinoma is also high in Southeast Asia, mainly because of the prevalence of hepatic schistosomiasis, Opisthorchis viverrini (Thai liver fluke), and Toxoplasma gondii in these regions, which are risk factors for cholangiocarcinoma.
Intrahepatic cholangiocarcinoma can develop in 7% of patients with intrahepatic bile duct stones. Bile-intestinal drainage can induce intestinal bacterial bile duct colonization and infection, which is also a risk factor for bile duct cancer. Polymorphisms in several genes have been identified to increase the risk of bile duct cancer and these genes can be classified as follows.
Proteins encoding proteins involved in cellular DNA repair (MTHFR, TYMS, GSTO1, and XRCC1).
Protection of cells against toxin resistance factors (ABCC2, CYP1A2, and NAT2).
Immune surveillance genes (KLRK1, MICA, and PTGS2).
The relationship between alcohol consumption and smoking and bile duct cancer has been reported inconsistently. According to the SSER (Surveillance, Epidemiologyand End Results) database analysis, metabolic syndrome increases the risk of intrahepatic bile duct cancer. Meanwhile, meta-analyses from the United States and Denmark suggest that diabetes and obesity increase the risk of intrahepatic cholangiocarcinoma, although researchers have speculated that obesity is a risk factor for cholangiocarcinoma, but evidence for this is so far insufficient.
Molecular mechanisms
With the advent of the era of individualized medicine and targeted therapy, there is a need to improve the understanding of tumor biology and molecular mechanisms of tumors. Carcinogenesis involves disruption of specific cellular genomes. Genetic pathways determine selective tumor growth, tumor differentiation and appreciation, and cell survival and can maintain genomic integrity. Modern research techniques can identify these genetic alterations in cholangiocarcinoma. However, in a retrospective analysis of molecular expression profiling techniques, earlier studies misclassified hilar cholangiocarcinoma as intrahepatic cholangiocarcinoma should be taken into account.
More in-depth studies could identify the mutated gene in cholangiocarcinoma, and targeted therapy against this gene could improve patient survival. However, it is difficult to find treatments for solid tumors because of the great heterogeneity among patients and drug resistance due to tumor gene evolution. So far, researchers have identified a number of signaling pathways involved in tumor formation and targeted drugs that target these pathways.
Studies on genetic alterations in cholangiocarcinoma have been reported, but most of them are only data from single studies and need further validation. Hopefully, individualized medicine and targeted therapies will be available for cholangiocarcinoma in the near future.
Cellular signaling pathways
The Ras-MAPK signaling pathway is one of the most prominent transduction pathways in the biology of cholangiocarcinoma and has been reported in several studies. For example, Sia and his colleagues analyzed the gene expression profiles of 119 cholangiocarcinoma patients and screened for two distinct groups of gene tags: proliferative and inflammatory classes.
The proliferative class is associated with differences in copy number of a number of oncogenes, including KRAS and BRAF signaling pathways, but also signaling pathways such as RAS, MAPK and MET. The proteins encoded by these genes form part of the RAS-RAF-MEK-ERK signaling pathway, which promotes cell proliferation or activates the PI3K-AKT-mTOR signaling pathway to promote cell survival.
Inflammatory-like signaling pathways activate inflammatory pathways that lead to overexpression of cytokines and STAT3. The transcription factor STAT3 regulates cell growth and survival and is involved in cellular carcinogenesis. In another study, researchers performing high-throughput expression profiling in patients with bile duct cancer after resection found that KRAS mutations were associated with abnormalities in the EGFR and ERBB2 (also known as HER2) signaling pathways. Abnormalities in genes involved in the regulation of proteasome activity were associated with poor prognosis.
Inhibition of tyrosine kinase inhibitors in cholangiocarcinoma cell lines activates both EGFR and HER2 signaling pathways. Although EFGR may act as a signaling factor to activate the RAS-MAPK, JAK-STAT and PI3K-mTOR pathways, it is more likely that there are interactions between the various tyrosine kinase receptors.
Researchers performing microarray analysis of 221 patients with extrahepatic cholangiocarcinoma found that genetic alterations in the tumor suppressor gene PTEN and activation of AKT or mTOR were associated with poor prognosis. However, in another study of 101 patients with intrahepatic cholangiocarcinoma, it was found that patients with genetic alterations of these genes had a good prognosis.
Cell growth and differentiation
Activation of the Notch signaling pathway, which plays an important role in cell growth and development and regulates bile duct formation, also plays an important role in the biology of cholangiocarcinoma, and can transform mature hepatocytes into precursor cells of intrahepatic cholangiocarcinoma. These studies challenge the theory that cholangiocarcinoma cells originate from bile duct epithelial cells, peri-glandular cells of the gallbladder, or hepatic precursor cells.
Cells of different origins of intrahepatic cholangiocarcinoma
The researchers also highlighted the plasticity of hepatocytes in different states of differentiation and paid attention to the transcriptomic study of overlapping imprinting of hepatocellular and cholangiocarcinoma. In an animal model, it was found that sustained activation of the Notch2 signaling pathway induced hypodifferentiated hepatocellular carcinoma and promoted the proliferation of bile duct epithelial cells during diethylnitrosamine induced hepatocellular carcinoma. The above studies suggest that even differentiated hepatocytes are plastic and different oncogenic pathways determine the cytohistological properties of different tumors (e.g. hepatocellular carcinoma, bile duct cancer).
Several experimental studies have shown that the Hh signaling pathway also plays an important role in cholangiocarcinoma and that inhibition of this pathway inhibits tumor growth. The mechanism includes inhibition of transcriptional activation as well as migration and miRNA expression. interactions between the Hh signaling pathway and the microenvironment of cholangiocarcinoma where fibroblasts accumulate have also been identified. In Hh-dependent in vitro environments and animal models, platelet-derived growth factor BB promotes tumor growth.
Isocitrate dehydrogenase (IDH) mutations and epigenetic alterations
Genetic alterations that promote cell growth can also lead to epigenetic alterations in the DNA code. Several research groups have recently found that hotspot mutations in genes encoding IDH1 and IDH2 proteins can lead to intrahepatic cholangiocarcinoma and some other gastrointestinal tumors (10-23%). These mutations are usually associated with DNA methylation, which can lead to epigenetic alterations.
The discovery of these mutated genes is of great interest because the product of IDH1 and IDH2 protease activity is 2-hydroxyglutaric acid, which is detectable in serum and can be used as a biomarker. Most importantly, inhibition of IDH protein gain of function reverses epigenetic methylation and promotes tumor cell differentiation. Cholangiocarcinoma may be treated with these inhibitors.
Cytotoxicity and targeted therapy
Empirical treatment regimens for gallbladder cancer were presented in the ABC-2 study, which included 410 patients with biliary tract tumors randomized to receive either gemcitabine + cisplatin combination chemotherapy or gemcitabine chemotherapy alone. The median overall survival was 11.7 months for patients receiving gemcitabine + cisplatin chemotherapy and 8.1 months for patients treated with gemcitabine chemotherapy alone. The regimen was effective in gallbladder and intrahepatic bile duct cancers. However, the effect of the combination chemotherapy regimen was limited.
Targeted therapies may improve the efficiency and safety of treatment, and some signaling pathways associated with gallbladder cancer may be potential targets. A number of clinical trials of targeted therapy or targeted therapy in combination with conventional chemotherapy regimens are currently underway. A randomized, open, single-center phase 3 trial comparing erlotinib in combination with gemcitabine + oxaliplatin to gemcitabine + oxaliplatin alone in gallbladder cancer found that patients treated with the combination of the targeted drug erlotinib had a longer median progression-free survival.
Intrahepatic cholangiocarcinoma
1.Clinical classification and diagnosis
Intrahepatic cholangiocarcinoma can be broadly classified according to morphological presentation into: mass type, periductal infiltrative type, intraductal growth type, superficial infiltrative type and undefined subtypes. The superficially infiltrating intraductal growth type has the best prognosis, while the mass type and periductal infiltrating type have the worst prognosis.
Intrahepatic cholangiocarcinoma usually presents as a malignant intrahepatic lesion. If the imaging presentation of cirrhosis is an intrahepatic lesion, the next step should be to identify whether it is cholangiocarcinoma or hepatocellular carcinoma. Imaging is an important tool to diagnose intrahepatic cholangiocarcinoma. Its characteristic manifestations include poorly defined lesions, dilated bile ducts, a few combined bile duct stones, and retraction of the lesion envelope.
The imaging characteristics of intrahepatic cholangiocarcinoma are as follows.
In ultrasonography, intrahepatic cholangiocarcinoma is mostly hypoechoic, and if the portal vein is invaded, the local duct wall and blood flow are mostly poorly displayed, this feature is obviously different from hepatocellular carcinoma and can be distinguished. In ultrasonography, ICC is mostly “fast in and fast out”.
In enhanced CT, ICC in the arterial phase is mostly irregular circular enhancement at the edge of the lesion, and gradually fills up centripetally in the portal phase and delayed phase, and low-density enhancement is common, and the central lower-density area may always be non-enhancing.
Hepatocellular carcinoma can present as both cholangiocarcinoma and hepatocellular carcinoma in the same node, which is called mixed hepatocellular-cholangiocarcinoma. Mixed hepatocellular-cholangiocarcinoma has its own unique presentation on imaging. Gadoxetic acid (gadoxetic acid)-enhanced MRI with rim enhancement and irregular shape suggests mixed hepatocellular-cholangiocarcinoma, while lobulated, weak rims suggest mass-like intrahepatic cholangiocarcinoma. The specific appearance also helps to distinguish mixed hepatocellular-cholangiocarcinoma from atypical hepatocellular carcinoma with less blood supply.
PET-CT is valuable in the diagnosis of metastatic disease, but many cholangiocarcinomas are not visualized on PET-CT. Compared with MRI and CT, ultrasonography has a high rate of misdiagnosis. Pathological biopsy is also required to distinguish hepatocellular carcinoma from intrahepatic cholangiocarcinoma, especially when the imaging of hepatocellular carcinoma is atypical.
CA19-9 is a commonly used serum marker for the diagnosis of cholangiocarcinoma. Patients with primary sclerosing cholangitis are highly suspected of intrahepatic cholangiocarcinoma if CA19-9 is >129 U/ml. The sensitivity, specificity and adjusted positive predictive value of this surveillance method are 79%, 98% and 57%, respectively. However, more than 30% of patients with primary sclerosing cholangitis with CA19-9 >129 U/mL did not develop intrahepatic cholangiocarcinoma during long-term follow-up. Among other things, bacterial cholangitis can also lead to elevated CA19-9 values.
CA19-9 >1000 U/mL is highly suspicious of advanced disease that has involved the peritoneum. The determination of CA19-9 values should also take into account the fact that some patients (about 7%) are negative for Lewis antigen. The above studies suggest that a better serum marker is needed to diagnose intrahepatic cholangiocarcinoma.
2. Surgical resection versus liver transplantation
Whether surgery is recommended for patients with intrahepatic cholangiocarcinoma requires the following considerations: biochemical characteristics of the tumor, size of the lesion, presence of metastases, and infiltration of blood vessels and lymph nodes.
Understanding the patient’s tumor load should also include imaging of the chest and abdomen and, if the lymph nodes are >2 cm, a lymph node biopsy. Patients with less than 30% of the mass with uninvolved margins of intrahepatic cholangiocarcinoma can be radically resected by surgery. Intentional management analysis reveals that patients with a mean survival time of 36 months should undergo surgical resection. Surgery is not effective if the following conditions are present: tumor margin involvement, lymph node metastasis, cirrhosis (especially advanced cirrhosis with a Child-Pugh score <5), and portal hypertension.
Although liver transplantation is recommended for some patients with hilar cholangiocarcinoma, the current study does not recommend liver transplantation for patients with intrahepatic cholangiocarcinoma. In fact, the recurrence rates of involvement at 1 and 5 years after liver transplantation in patients with mixed hepatocellular-cholangiocarcinoma are 42% and 65%, respectively.
3.Palliative care: local area therapy
As with hepatocellular carcinoma, the common site of metastasis in intrahepatic cholangiocarcinoma is the liver; therefore, local area therapy may be an effective treatment option, but to date there are no high-quality randomized studies to support this therapy. Radiofrequency ablation also has its limitations, with limited effect on lesions >5 cm and tumors close to large blood vessels and liver capsule sites; even with radiofrequency ablation, the chances of recurrence remain high.
Most studies on transhepatic artery chemoembolization (TACE) are retrospective and do not use standardized chemotherapeutic agents or regimens. However, study data suggest that patients treated with TACE are well tolerated and may improve patient survival. Drug-eluting microsphere-TACE (DEB-TACE) may have similar efficacy to systemic chemotherapy and better results than conventional TACE.
With regard to the use of ? Y for selective intra-arterial radiotherapy has been reported recently, with a median overall survival of 22 months and no major toxicity-related events. Another study reported that ? Y treatment resulted in a 1-year survival of 56%. Modern stereotactic radiotherapy for bile duct cancer can cause the following complications: abnormal liver function due to acute radiotherapy, bile duct stricture and gastrointestinal mucosal injury.
Cholangiocarcinoma of the liver portal
1.Clinical classification and diagnosis
Hepatoportal cholangiocarcinoma refers to bile duct mucosal epithelial carcinoma involving the common hepatic duct, the left and right hepatic ducts and their confluence. The intraductal type can be subdivided into periductal infiltrative type (the most common type of hilar cholangiocarcinoma), mass type and nodular type. Intraductal ductal papillary cholangiocarcinoma is often well differentiated and has a better prognosis, but is more likely to metastasize. A recently identified type of ductal papillary cholangiocarcinoma has a better prognosis than the exophytic type of hilar cholangiocarcinoma.
The first symptom in 90% of patients with cholangiocarcinoma is an acute onset of painless jaundice. Imaging and ultrasound endoscopy can help distinguish the location, size, morphology, hepatic artery and portal vein involvement, future residual liver volume, the presence of lymph node metastases, and the presence of distant metastases. Imaging has a limited role in hilar cholangiocarcinoma.
CT scans often fail to detect whether the peritoneum is involved. MRI examinations are similar to CT in detecting dilatation of proximal and narrow bile ducts and periportal masses, but magnetic resonance cholangiography (MRC) adds another dimension to the study and better determines the extent of biliary lesions. the sensitivity and accuracy of MRC-enhanced MRI are 89% and 76%, respectively.
If liver transplantation is possible in patients with hilar cholangiocarcinoma, tumor sampling cannot be performed simultaneously with ultrasound endoscopic evaluation of the patient’s condition prior to transplantation because of the significant risk associated with needle diameter implantation; this limits this procedure to some extent. In contrast, fine needle aspiration of lymph nodes is of great value in the diagnosis of advanced hilar cholangiocarcinoma.
CA19-9 values have a similar role in the diagnosis of hilar cholangiocarcinoma as intrahepatic lesions. In addition to this, IgG4 serum concentration should be checked to exclude IgG4-related biliary lesions; however, serum IgG4 concentration can also be elevated in cholangiocarcinoma. Endoscopic retrograde cholangiography (ERCP) is very important in the initial evaluation of the biliary system and is the first treatment.
Cholangiography should be guided by endoscopy before localization with MRI/MRC or CT (or a combination of both). If strictures are present, cytology should be performed regardless of whether the upstream bile duct is dilated. There are traditional methods of cytology and, if available, fluorescence in situ hybridization (FISH). FISH allows direct hybridization to chromosomes thereby localizing specific genes on chromosomes, and this method of examination can increase the sensitivity of traditional cytology from 15% to 38-58%.
2. Surgical treatment and liver transplantation
The newly proposed surgical staging system can guide the surgical plan and screen the patients suitable for surgery. The procedure is quite complex, requiring lobectomy and bile duct resection, regional lymph node dissection, and Roux-Y surgery. The surgical techniques are increasingly sophisticated and computer-assisted lobectomy, revascularization and preoperative portal vein embolization are now available.
This procedure promotes the proliferation of undamaged lobes and increases the volume of the residual liver. The success of the procedure depends largely on the vascular anatomy. Portal vein ligation and in situ hepatic splitting promote rapid hepatocyte proliferation. However, this technique has high morbidity and mortality rates and requires further evaluation. Whether stenting should be implanted prior to surgery remains to be discussed. In patients who cannot undergo surgery, resection of 50% or more of the liver parenchyma may improve patient survival.
Plastic bile ducts or laminated self-expanding metal stents should be placed before treatment options for hepatoportal cholangiocarcinoma are determined. Overlying stents may stop tumor growth but may lead to tumor metastasis and increase the incidence of acute cholecystitis and pancreatitis. Liver transplantation with radiotherapy is the best approach for advanced cancer, but only a small percentage of patients are candidates for surgery. The criteria for surgery include unresectable hilar cholangiocarcinoma >3 cm in diameter without intra- or extra-hepatic metastases, and a 5-year recurrence-free survival rate of 68% after surgery. Patients with hilar cholangiocarcinoma combined with primary sclerosing cholangitis should have active liver transplantation.
Treatment of advanced bile duct cancer
If patients are not suitable for surgery or liver transplantation, gemcitabine + cisplatin chemotherapy should be considered. However, in the ABC-02 study, the combination of gemcitabine + cisplatin did not significantly improve the survival rate of patients with hilar cholangiocarcinoma.
Appropriate preparation, including biliary stent placement, should be performed prior to chemotherapy. Metal stents should be used if palliative therapy is used and the patient has a survival goal of no more than 4-6 months because they are more durable, less invasive to the patient, and more cost-effective compared to plastic stents. Also, metal stents may improve patient survival compared to plastic stents.