Investigation and Diagnosis of Oesophageal Cancer
Oesophageal cancer, also referred to as cancer of the gullet or food pipe, has become increasingly common in the past 30 years and is currently the sixth leading cause of cancer death worldwide. (1,2) Patients may present with weight loss and dysphagia. Dysphagia usually occurs late in the course of the disease when the lumen of the oesophagus has been narrowed by 50-75%. This is the most common symptom and is followed by weight loss. Other symptoms include stridor, cough and aspiration pneumonia as the result of erosion into the transbronchial tree. This is a sign of unresectability. Other signs of unresectability are hoarseness, caused by invasion of the recurrent laryngeal nerve. Jaundice and bone pain are symptomatic of organ metastases. (PC1, PC2)
The normal oesophagus is lined by non-keratinising stratified squamous epithelium. The most common types of oesophageal cancer are squamous cell carcinoma and adenocarcinoma. (PC1)
Squamous Cell Carcinoma (SCC)
Squamous cell carcinoma arises in cells that line the upper and middle part of the oesophagus in response to various risk factors.(3) 60% of cases occur in the middle third of the oesophagus, 30% of cases occur in the lower third and the remainder of cases occur in the upper third or post-cricoid region of the oesophagus.(BOOK IP) It spreads to local nodes first and then to liver and lungs.(BOOK rrp) Microscopic features of squamous cell carcinoma include dysplastic squamous epithelium, dense fibrous stroma, keratin pearl formation and intracellular bridging. (BOOK IP)
Adenocarcinoma is most common in the mid and distal oesophagus. It arises from abnormal oesophageal mucosa in a well-characterised sequence. Metaplasia of the normal epithelium of the distal oesophagus occurs in reaction to chronic gastroesphageal reflux. This metaplasia results in a specialised intestinal glandular epithelium containing goblet cells, called Barrett epithelium. Further genetic alterations of this epithelium leads to dysplasia, which may progress from low-grade to high-grade dysplasia and then, ultimately, to adenocarcinoma. (PC1) Microscopic features of adenocarcinoma include severely dysplastic glandular structures, signet ring cells and dense fibrous stroma. (BOOK IP)
Prevalence of Oesophageal Cancer
Ireland and UK
Each year, about 300 people in Ireland learn that they have cancer of the oesophagus. Statistics from the National Cancer Registry show that in 2007 in Ireland, there were 402 registered cases of oesophageal cancer. Of these, 139 were female cases and 263 were male cases. UK statistics show that since the 1970s, oesophageal cancer rates in women have increased by nearly a fifth, compared with an increase of more than 50% in men. Between the years 2005 and 2007, the rate per 100,000 population of oesophageal cancer in Ireland was 5.31 in females and 12.32 in males. This is also similar to findings in the UK for 2006 with female rates being 5.7 and male rates being 14.1. These statistics show that there is a much higher prevalence of oesophageal cancer in men. Statistics also show that two-thirds of patients diagnosed with oesophageal cancer in Ireland between 1994 and 2007, were over 65 years of age at diagnosis. UK statistics are similar to this with 8 in 10 oesophageal cancers occurring in people aged 60 or over. (5,6,7)
Oesophageal cancer is the sixth leading cause of cancer death worldwide, with the highest incidence rates in China, Japan and northern east Asia. (BOOK IP) Incidence if oesophageal cancer can be as high as 30-800 cases per 100,000 persons in particular areas of northern Iran, some areas of southern Russia and northern China. (PC2) Oesophageal cancer is 50% more common in African-Americans than in whites. Squamous cell carcinoma is relatively more common in African Americans. In contrast, adenocarcinoma is more common in white Americans. (PC1) Squamous cell carcinoma of the oesophagus is the most common primary cancer in developing countries. (BOOK) Oesophageal adenocarcinomas have become increasingly common and the rate of these tumours has increased dramatically and more rapidly than any other solid malignancy in the United States. In contrast to this, the incidence of oesophageal squamous cell carcinoma has declined in the US but worldwide it is responsible for 95% of all oesophageal cancers. (4,PC2) Adenocarcinoma has its highest incidence in northern Europe. (BOOK IP)
Like many cancers, the exact cause of oesophageal cancer is unknown, but there are many factors that can increase risk. The risk of getting oesophageal cancer increases with age and, as seen in the statistics previously mentioned, most people who develop it are over the age of 60. Also, as seen from statistics, it has a higher prevalence in men than in women, with men being almost three times more likely to develop it. Tobacco products increase the risk of oesophageal cancer and this combined with long-term excessive alcohol consumption leads to an even greater risk. Obesity increases risk of adenocarcinoma of the oesophagus. Diets lacking in fruit and vegetables along with vitamins A, C and Riboflavin may also increase the risk of developing oesophageal cancer. Research has shown that smoking, excess alcohol and a low intake of fruit and vegetables cause approximately 9 out of 10 squamous cell carcinomas of the oesophagus. Smoking, overweight and obesity, low fruit and vegetable consumption along with acid reflux has been estimated to account for 8 in 10 adenocarcinomas of the oesophagus. Frequent drinking of hot drinks is also thought to increase the risk of this cancer. There are some occupational exposure risk factors such as long-term exposure to the chemical perchloroethylene, which is used in dry cleaning solvents. Radiotherapy to the chest area and certain medical conditions have been linked to an increased risk of oesophageal cancer. Reflux disease or Gastroesophageal reflux disease (GORD) is a risk factor for cancer of the oesophagus. Although heartburn is one of its main symptoms, GORD can also arise without symptoms and a long-term exposure to reflux increases the risk of this cancer. Squamous Cell Carcinoma of the oesophagus has been associated with achalasia. This is a condition in which the lower oesophageal sphincter does not relax and therefore food is retained in the lower oesophagus. This retained food along with the tight sphincter causes the lower oesophagus to dilate and about 6% of patients with this condition develop squamous cell carcinoma of the oesophagus. There are also some rare congenital causes of oesophageal cancer. Plummer-Vinson syndrome is characterised by anaemia, oesophageal welding and abnormalities of the tongue, fingernails and spleen. Patients with this syndrome have a 1 in 10 lifetime risk of developing squamous cell carcinoma. Tylosis, a rare autosomal dominant skin disease, is characterised by excessive thickening of the plantar and palmer skin surfaces and it is associated with a 40-95% lifetime risk of developing oesophageal squamous cell carcinoma. (4,5,6)
Barrett's oesophagus was first identified by N.R. Barrett in 1950. He first described the replacement of the normal squamous mucosa of the distal oesophagus by a columnar epithelium of both gastric and intestinal types.(PC3) It is defined by columnar mucosa of at least 2cm length appearing within the anatomical oesophagus. (BOOK IP) It is an acquired condition and it is estimated that 1% of the UK population have Barrett's epithelium, with only 1 in 20 of these diagnosed. (8,9)
Barrett's oesophagus is a consequence of prolonged GORD. It appears predisposed to oesophageal adenocarcinoma, which has a rapidly increasing incidence rate in most western countries. Tumour progression is characterised histologically by the metaplasia-dysplasia-carcinoma sequence. (8,10)
Diagnosis of Oesophageal Cancer
Early diagnosis is vital and it is important to note that superficial lesions are often only associated with non-specific symptoms related to gastro-oesophageal reflux.(9) Patients may present with clinical symptoms such as dysphagia, weight loss or poor appetite, pain or discomfort behind the breastbone or between the shoulder blades, discomfort in the throat or back, acid indigestion or heartburn that does not cease, frequent hiccoughs or belching, ongoing cough or vomiting. (5) Acute haemorrhage, iron-deficiency anaemia and respiratory symptoms due to aspiration or fistulation into the respiratory tract are less common presenting features of advanced disease.(9)
Diagnosis of oesophageal cancer is mainly carried out by endoscopy. An endoscope allows the doctor to look at the inside of the oesophagus and also allows the doctor to take biopsies of any areas that appear abnormal. One of the challenges in the endoscopic diagnosis of oesophageal cancer is the early detection of early neoplastic lesions in patients with a known Barrett's oesophagus. A study evaluating the various endoscopic techniques used in the diagnosis and staging of oesophageal cancer found that the optimal endoscopic imaging of Barrett's oesophagus requires the use of high-resolution endoscopy with a low threshold to biopsy all abnormalities no matter how delicate they appear. New endoscopic imaging modalities hold the promise of better endoscopic detection of early cancer and its precursor lesions in Barrett's oesophagus. Video-autofluorescence and narrow band imaging are the most promising techniques in this respect and can be used an a “red flag” technique drawing attention to potentially neoplastic areas. Although its limitation is a high rate of false positive results. (12)
Another test that may be carried out in the diagnosis of oesophageal cancer is Barium Swallow. This is a special X-ray of the oesophagus. The patient is required to drink barium, a white chalky liquid, and a series of X-rays are taken as it passes down the throat into the stomach. The barium outlines the oesophagus and will show up abnormalities on the X-ray. (5,11)
One of the most important aspects of diagnosis is accurate staging at the time of commencing treatment, since this provides the basis for measuring the treatment and prediction of long-term outcome. (13) Staging involves testing to find out the exact size of the tumour and whether it has spread to other parts of the body. The TNM classification, as seen in the table below, is well established and is widely used in the staging of tumours. This classification includes the depth of oesophageal wall penetration by the primary tumour (T factor), the presence of regional lymph node metastases (N factor) and distant lymph node or organ metastases (M factor). Distant lymph node metastasis is classified as M1a according to tumour location, metastasis in coeliac nodes for tumours of the lower thoracic oesophagus and metastasis in cervical nodes for tumours of the upper thoracic oesophagus.(5,13)
Tis, carcinoma in situ (high grade dysplasia); T1, invading mucosa/submucosa; T2, invading muscularis propria; T3, invading adventitia; T4, invading adjacent structures.
*M1a, coeliac node metastasis from a lower-third tumour
**M1b, non-regional lymph node or other distant metastasis.
Table 1: International Union Against Cancer tumour node metastasis (TNM) staging for oesophageal carcinoma (fifth edition) (9)
Various further tests are required for the staging of oesophageal cancer.
Endoscopic Ultrasonography (EUS)
Endoscopic ultrasonography (EUS) is superior to any other imaging technique in the assessment of local tumour infiltration of oesophageal adenocarcinoma and locoregional lymph nodes status. (12) This test is similar to an endoscopy. A small ultrasound probe is connected to the scope while in the oesophagus and sound waves are then used to give a picture of the body from inside the oesophagus.(5) According to a study, the reported accuracy of EUS in detecting the T stage is almost 85% and it has a reported accuracy of 75% in detecting the N stage. (13) EUS allows for the identification of patients with advanced disease who are unlikely to benefit from attempts at curative surgery and in whoa a conservative palliative treatment is indicated. EUS should be performed in all operable patients in whom no distant metastases are found on CT-scanning and ultrasound of the neck. (12) The current recommendation for staging oesophageal cancer is a combination of EUS and Computed Topography (CT). (9)
Computed Tomography (CT)
CT scanning has a major role in identifying liver and lung metastases. As it cannot differentiate the individual layers of the oesophageal wall, it is of little value in determining the depth of wall penetration. However, it can demonstrate the invasion of the tumour into the adjacent organs in advanced cases. This invasion is usually evaluated by the presence or absence of a visible fat layer between the surrounding organs and the tumour. Several groups have compared EUS with CT for oesophageal cancer staging and have found EUS to be significantly superior in correctly predicting the T classification. However, the definitive exclusion factor for endoscopy is severe stenosis. Under this condition, CT is a superior diagnostic tool to EUS. (13)
Magnetic Resonance Imaging (MRI)
The accuracy of MRI is equal to that of CT. The value of it in the staging of oesophageal cancer is still questionable as CT is more accessible and less expensive. (13)
Positron Emission Tomography (PET)
Conventional imaging methods, including those mentioned above, determine the extent of disease based on associated morphologic changes. PET, however, yields physiological information that provides a mean for diagnosing cancer based on alterations in tissue metabolism. Various studies have shown PET to be superior to other techniques in detecting metastases. Flanagan et al. showed that PET revealed metastatic disease among five patients in whom CT did not. Luketich et al. found that PET detected nine sites of distant metastases missed by conventional screening, including CT, EUS and bone scan. Block et al. reported that PET identified metastatic disease in all 17 patients, whereas CT was positive for metastases in only five cases. PET predicted the metastatic involvement of adjacent lymph nodes in 52%, almost twice as many as CT scanning which was 29%. PET improved the rate of detecting distant disease that was not identified by CT alone. (13) Both bone sitigraphy and PET scanning have been found to detect metastases in patients who were thought to be free from distant disease following conventional staging. Although these numbers detected are small, the potential savings of avoiding inappropriate surgery, both in terms of morbidity to the individual and cost to the health service are significant. As CT PET scans are become more available, they are likely to become a key part in the staging process of oesophageal cancer. In the meantime, bone scans are part of the staging process for patients with more advanced disease being considered for surgery. (9)
Histology correlates Lugol's staining intensity with the content of glycogen in the superficial squamous mucosa. Most of the unstained areas are carcinomas or high-grade dysplasia. Carcinomas also have a sharply demarcated border. In contrast, low-grade dysplasia tends to be lightly stained with an indistinct margin.(14) Lugol's iodine has been used with endoscopy in a procedure known as Lugol chromoendoscopy. This has been used to detect early oesophageal cancer, which is difficult to detect by routine observation without dye staining. A study has shown that this procedure also has the potential for the diagnosis of so-called endoscopy negative GORD. In this study, following the absence of any oesophageal mucosal abnormalities during conventional endoscopy, Lugol's iodine was sprayed onto the oesophageal surface. The staining pattern was then observed. Visible unstained streaks by Lugol chromoendoscopy seem to be indicative of mucosal injury, which was not detectable by the conventional endoscopy. (FRENCH COMP)
35βH11 does not stain oesophageal squamous cell carcinoma. In contrast, AE1/AE3 usually stains positive in squamous cell carcinoma. Approximately 85-100% of squamous cell carcinomas react positively to CK19. This staining response depends greatly on the grade of tumour. Almost all squamous cell carcinomas are negative to both CK7 and CK20 when a positive result is defined as staining in >50% of the neoplastic cells. CK5, especially the D5/16B4 clone, stains almost all squamous cell carcinomas. Cytoplasmic staining of involucrin and thrombomodulin can also be seen in squamous cell carcinomas.
CK7, CK20 and CK5 are useful in differentiating between squamous cell carcinoma and adenocarcinoma. Most squamous cell carcinomas are CK7-, CK20- and CK5+, whereas adenocarcinomas of the oesophagus are almost always CK7+, CK20+ and CK5-.(DABBS)
Molecular aspects of oesophageal cancer
p53 is a tumour suppressor protein that in humans is encoded by the TP53 gene. p53 regulates the cell cycle and thus carries out its function as a tumour suppressor gene by preventing cancer. Deletion or mutation of tumour suppressor genes has been found to be a key event in tumourigenesis. Frequent mutation of the p53 gene at exons 5,6,7 and 8 have been found in a wide variety of human cancers including oesophageal squamous cell carcinoma. Mutated p53 proteins are more stable than the wild type and therefore their accumulation can be detected immunohistochemically.
In a study by Li-Dong Wang et al. in 1993, the accumulation of p53 protein in precancerous lesions of resected oesophagi from SCC patients and assymptomatic subjects from a high-risk population was analysed in order to gain insight into the possible involvement of p53 protein in the early stage of oesophageal cancer. The study showed that p53 protein accumulated with increasing frequencies in the proliferating cells in basal cell hyperplasia (BCH), dysplasia, carcinoma in situ (CIS) and squamous cell carcinoma. These findings prove p53 as a possible early biomarker for carcinogenesis. (20)
In another study, carried out by King Y.Lam et al. in 1997, the prevalence and predictive value of p53 mutations in SCC patients was analysed. This study was carried out using immunohistochemistry and polymerase chain reaction (PCR) with single-strand conformational polymorphism (SSCP). p53 over-expression was detected immunohistochemically in 73% of the patients. Using the PCR-SSCP technique to screen for mutations in exons 5,6,7 and 8, mutations were detected in 44% of the patients. 82% of these mutations were found to be point mutations. In patients with stage III oesophageal cancer, the median survival of those with p53 mutations was 6.8 months whereas those without was 12.5 months. This therefore shows that there is a definite role of p53 in the pathogenesis of oesophageal SCC and that p53 mutations also appear to play a role in predicting the survival of patients with stage III oesophageal SCC. (21)
In 2003, a study looked at the common genetic variants of TP53 and BRCA2 in patients with oesophageal cancer and also healthy individuals from areas of high and low risk in northern China. SSCP and DNA sequencing were used to assess and compare frequencies of R72P (TP53) and 5'UTR203G>A, N372H and K1132K (BRCA2) in the groups of individuals mentioned previously. The most significant outcome of this study was that the difference in the distribution of genotypes by risk groups for 203G>A was due to a low prevalence of genotype GG in oesophageal SCC patients. This is consistent with a disease association and the findings suggest that the 203G>A polymorphism in BRCA2 may be associated with the risk of oesophageal SCC. (22)
Another study looked at the immunoexpression of p53 in the oesophageal mucosa of smokers and alcohol consumers and its relationship with different degrees of histological findings. It also looked at the role of Lugol chromoendoscopy in the detection of areas expressing p53. They found that alcoholics/smokers were 1.9 times more likely to express p53 than non-alcoholics/non-smokers. Overall, they found that there was an association between histological changes, p53 expression and Lugol's unstained areas. This may point to a higher risk of oesophageal SCC. Smokers and alcohol drinkers with normal mucosa or chronic oesophagitis, who express p53 protein, may represent an unrecognised sub-group of individuals that may benefit from a screening programme to identify precursor lesions of oesophageal SCC.(23)
Minichromosome maintenance (MCM) protein dysregulation is characteristic of early epithelial carcinogenesis. The key DNA replication initiation factors associated with this can be used as diagnostic markers for cervical and genitor-urinary tract cancer. A study has proved that elevated levels of Mcm5 in gastric aspirate samples are highly predictive of oesophageal cancer. The test carried out in this study used immunofluorometric assay to measure Mcm5 levels in cells located from the gastric aspirates. This test is readily automated and has great potential in primary diagnosis, surveillance and screening of oesophageal cancer. (24)