The colon and rectum are continuous and cancers affecting them are referred to as colorectal cancers. Rectal cancer causes nearly 50,000 deaths a year in the U.S alone. Nearly 2/3 of colorectal cancers occur in the colon while about 1/2 occur in the rectum. In fact, colorectal cancers are the third-leading cause for cancer deaths in the U.S. after lung cancer and breast cancer. Typically colon cancer starts as small adenomatous polyps that later turn cancerous. Incidence of colorectal cancer is higher in Western nations as compared to Asian and African countries. More men tend to get affected by this form of cancer than women. Often hereditary syndromes cause multiple polyps in the digestive tract. Environmental and genetic factors play a large role in the occurrence of colorectal cancers. Those suffering from inflammatory bowel disease or ulcerative colitis have an increased risk of developing colorectal cancers.
Rectal cancers do not produce symptoms in the initial stages. They can be detected only by digital or proctoscopic screening tests. If you notice blood in your stools or change in the shape of the stools or cramping pain in the lower abdomen, visit a doctor to check for signs of colorectal cancer. Patients may notice change in bowel habits and urinary symptoms. Stools may be narrower and often black and tarry. A feeling of bloating or colic pain may be experienced on account of obstruction due to tumor. Sometimes there is bowel perforation accompanied by fever and pain. Weight loss, fatigue and anemia may result.
A digital rectal examination helps in detecting abnormal lesions. Any tumor can be assessed for size and ulceration. Laboratory tests and screening procedures such as x-rays and Endoscopy aid in visualizing the lining of the colon. Since the risk of colorectal cancer increases with age, the American Cancer Society recommends yearly digital examination of the rectum for those above 50 years. Any abnormal lesions in the rectum are examined and a biopsy is performed. If a diagnosis of rectal cancer is established, staging has to be established to determine the depth of tumor penetration. Staging aids the physician in determining the treatment options. Rectal cancers are divided into 4 stages. In the first 2 stages and suspected stage 3 state, surgery is used to remove the affected part of the rectum along with its vascular and lymph. Radiation and chemotherapy are also resorted to. Radiation therapy helps in shrinking the tumor prior to surgery. Rectal cancer is often linked to diets rich in fat and calories and low in fiber. Colon cancers can be prevented with the right diet and lifestyle. Diets rich in unsaturated animal fats and highly saturated vegetable oils are known to cause colorectal cancers. High-fiber food helps in the formation of soft and bulky stools, diluting carcinogens and decreasing colonic transit time. This allows lesser chance for polyps to develop. Other dietary elements such as calcium, selenium, carotenoids and vitamins A, C and E help in destroying dangerous free radicals in the colon.
Cancer of the Head and Neck
Head and neck cancers can be of many types, based on the area where they are found.
Symptoms of head and neck cancer can range from a lump in the neck to hoarseness of voice to even a growth in the mouth. A person may notice a change in voice. A person suffering from mouth and tongue can lead to sores. Basal cell cancer of the skin is another form of head and neck cancer. Early detection of head and neck cancer is vital to timely treatment. Most of these cancers lead to identifiable symptoms. Blood in the saliva or phlegm can indicate mouth, nose or throat cancer. Persistent earache and difficulty in swallowing can be due to infection or tumor in the throat. Cancer of the nasal cavity can result in nose blockage, pain in the forehead and face numbness.
Most common causes for head and neck cancers are smoking, chewing tobacco and alcohol. Other probable factors for head and neck cancer are are HPV infection, asbestos exposure and excessive sun exposure. A person suffering from Epstein Barr virus is at higher risk for developing head and neck cancer. Do not ignore a persistent lump on the neck or tongue or jaw. Consult a doctor when you notice difficulty in swallowing for more than a few weeks.
A doctor will conduct a physical examination and probably take a biopsy of any suspicious lymph nodes or tissues. If a cancer of the head or neck is detected, further tests will be needed to judge the extent of spread. The type of treatment usually depends on the extent of spread of the tumor.
Immunohistochemicalmarkers (IHC markers) act as precursors for the identification of cancers or tumors in the body. They are made up of monoclonal antibodies which determine the target-specific proteins present in the respective tissue. These antibodies adhere to the proteins which are indicated by using stains. The diagnostic approach by using immunohistochemicals effectively identifies the type of protein to determine the histological changes of a specific tumor or cancer when identified. It also helps in the identification and categorization of homogeneous malignant tumors.
Specimen preparation for IHC
In the IHC technique, signal amplification and visualization is generally used and hence the selection of appropriate antibodies to target the antigens is very important. In addition to this the cell morphology, tissue design and antigenicity is also taken in to consideration. The tissues obtained are preserved carefully to prevent cellular damage and tissue morphology. Tissue fixation is done using formaldehyde as it enables proper adherence in preventing the onset of target antigen masking. In order to avoid the nonspecific protein site binding by the antibodies, the specimens are kept in buffer solutions such as bovine serum albumin, serum and non-fat milk in dried form.
The important principle administered in the immunohistochemical technique is based on the antigen-antibody reaction. The monoclonal antibody administered in the process binds to the tissue antigen for a complex with the help of secondary enzyme-conjugated antibody in the presence of a substrate and a chromogen for colored identification. The enzyme forms deposits at the site of antigen and antibody complex which can be determined by using computerized mechanisms to identify the locus of the tumor or cancer if present through protein determination.
The detection antibody plays a very significant role in the process of IHC technique. The categories of antibodies used vary from monoclonal to polyclonal which is determined by the type of diagnosis. Monoclonal antibodies identify single epitopes pertaining to linear or conformational in origin. The specificity of monoclonal antibody administration is seen in lower backgrounds and of polyclonal antibodies is seen in high backgrounds. Monoclonal antibody in tissues is administered overnight with a concentration of 5-25 micrograms/ml at 4°c whereas polyclonal antibodies are administered in the concentration of 1.7-15 micrograms/ml at 4°c.
The concentration of monoclonal antibodies and polyclonal antibodies for cells is similar to tissues but the duration of time is one hour at room temperature. Despite many advantages, monoclonal antibodies have disadvantages with respect to vulnerability in epitope masking and polyclonal antibodies have accumulation of heterogeneous population. The results of IHC antibody administration is carried on using various combinations.
The following proteins are identified in various tissues by using the antibodies. 1. Vimentin is a filament predominantly expressed in the connective tissue tumors and melanomas.
2. Leukocyte common antigen which is significantly found in leukemia and lymphomas.
3. CD 20 which is found in B-lymphocytes and CD3 found in T-lymphocytes.
4. Smooth muscle actin an important intermediate filament - This marker is usually expressed in myofibroblastic and myoepethelial cell tumors.
5. Cytokeratins are also used in the detection of adenocarcinomas and other carcinoma. The combinations of cytokeratins include both low molecular and high molecular weight compounds.
Complications in the IHC technique
IHC markers are very important in the determination of target therapies for cancers and tumors. The most common problem encountered in the immunohistochemistry technique is the background staining. Background staining is related to unwanted specific staining when mediated by interactions of antibodies and their respective epitopes and also nonspecific staining for all other interactions. The incidences of background staining are generally blocked by using reagents such as peroxidases.
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Bibliography / Reference
Collection of Pages - Last revised Date: February 23, 2020