Colorectal (colo = colon; rectal = rectum) cancer, is assessed to be the fourth most frequently diagnosed cancer and the second leading causes of cancer-related deaths. According to an estimate, colorectal cancer accounted for about 10% of all incidents and mortality of cancer in 2010, in the United States. The overall incidence and mortality of colorectal cancer have been declining steadily during last few decades. However, the incidence rate of colorectal cancer has significantly increased over the last two decades in patients with age between 20 to 49 years.
The large intestine consists of mainly 4 regions: cecum, colon, rectum, and anal canal. The colon, which forms the major part of large intestine, is further divided into 4 main portions: ascending colon, transverse colon, descending colon, and sigmoid colon. The next about 15 cm long continuation of the colon is termed as the rectum.
What is the function and anatomy of human colon?
The main functions of colon and rectum include final digestion and absorption of food with the help of bacteria commonly found in these parts and production of some vitamins.
Colon or large intestine consists of various parts like caecum, ascending colon, transverse colon, descending colon, and sigmoid colon.
If we see the cross section of colon wall, the various layers from inside out are epithelium, lamina propria, muscularis mucosa, submucosa, muscularis propria, pericolorectal tissues, and serosa.
Adenocarcinoma (affecting mucosal cells that lines the innermost lining of the large intestine) is the most commonly encountered (more than 95% of all cases) colorectal cancer.
What is the Staging of Colon Cancer?
Tis – tumor is limited to the epithelium
T1a – tumor infiltrates into the lamina propria or muscularis mucosa
T1b – tumor infiltrates into the submucosa.
T2 – Infiltration into muscularis propria
T3 – Pericolorectal tissue infiltration
T4a – Infiltration of serosa
T4b – tumor infiltrates through the wall of colon, to involve the surrounding structures
T4b disease from any part of colon may involve the small intestine.
T4b tumor from ascending colon may involve the right kidney.
And from the transverse colon may involve left kidney.
N0 – No involvement of regional lymph nodes
N1 – Involvement of 1 to 3 nearby lymph nodes by tumor
N2a – Involvement of 4 to 6 nearby lymph nodes by tumor
N2b – Involvement of >/=7 nearby lymph nodes by tumor
M0 – Cancer has not spread to distant sites
M1a – Cancer has spread to one distant organ without peritoneal spread.
Like in this figure, it has spread to liver.
And here it has spread to lungs.
M1b – Cancer that has spread to >/=2 distant organs without peritoneal spread.
Here, colon cancer has spread to both lungs and liver.
M1c – Cancer that has spread to peritoneum with or without other sites.
This figure shows tumor spread to peritoneum.
What is the Stagewise Treatment of Colon Cancer?
Treatment of colon cancer depends on stage of tumor, presenting signs and symptoms, preoperative CEA levels, presence or absence of genetic abnormalities, performance status, along with other factors. But the final treatment decision is taken by the oncologist after clinical evaluation of the patient.
Stage I (T1 and T2, Node Negative)
Surgical resection of colon, in the form of right or left hemicolectomy is the mainstay of treatment in these cases.
There is no role of adjuvant or postoperative chemotherapy in such cases.
Stage II (T3 and T4, Node Negative)
In stage 2 also, surgical resection is required for all cases. In T3 disease, postoperative chemotherapy is recommended in high-risk disease, as assessed by the oncologist. Whereas, chemotherapy is required in all cases of T4 disease after surgery.
Stage III (Node Positive Disease)
In node positive disease also, postoperative chemotherapy is recommended in all the patients after surgery.
Stage IV (Metastatic Disease)
Treatment of metastatic disease depends on whether it is resectable or non-resectable.
Non-Resectable Metastatic Disease
Most cases of metastatic disease are treated with chemotherapy with/without targeted therapy. Immunotherapy is also an option for treatment of metastatic colon cancer.
Resectable Metastatic Disease (Is Resection possible even in the case of Metastatic Disease?)
In some selected cases, with limited metastasis to liver and/or lungs, tumor resection may be possible. Also in unresectable disease, it may become resectable if it responds nicely to treatment.
Like in this figure, when limited liver metastasis involves only a small part of liver, surgical resection may be tried.
Similarly, if lung metastasis is localised to only a small part, that can be removed safely, resection may be done.
What is the role of Ablation or Embolization for Liver Metastasis?
These techniques also are used when liver metastasis are limited to a small part that can be subjected safely and effectively to such modalities.
Embolization is a process in which liver metastasis are addressed by injecting certain chemicals into the hepatic artery. It may be called radioembolization, chemoembolization or arterial embolization depending upon the type of substance used for the procedure.
In arterial embolization, inert particles are used, whereas, particles are loaded with drugs in chemoembolization, and with radioactive substances in radioembolization). This technique is mainly used for destroying liver metastasis, if patient is a suitable candidate for the same.
Similarly, Ablation is a technique in which tumor is destroyed without actual removal from the body. This technique is mainly used for destroying liver metastasis, if patient is a suitable candidate for the same. It may be called radiofrequency ablation, cryoablation, microwave ablation or percutaneous ethanol injection depending upon the technique
High-energy radio waves are utilized in radiofrequency ablation (RFA), microwaves are used in microwave ablation (MWA) technique, while very cold gases are used in cryoablation to destroy tumors. Sometimes, an ethanol injection given directly into the tumor tissue can be used to kill tumor cells. Imaging techniques are utilized along with these ablation techniques to accurately locate the target tumors.
What is the role of Targeted Therapy for Colon Cancer Treatment?
Targeted drugs are designed to target a specific gene or protein characteristic of colon cancer cells. With advancements in diagnostic techniques, a number of genetic abnormalities for colon cancer have been identified that can be targeted with the help of targeted drugs.
Molecular testing to confirm the genetic abnormality is the pre-requisite for starting a targeted therapy. They work differently than chemotherapy drugs that they target a specific gene or protein characteristic of the cancer cells. For example, Cetuximab and Panitumumab target epidermal growth factor receptor (EGFR) protein, Bevacizumab targets vascular endothelial growth factor (VEGF) receptor. They are generally used alone or in combination with chemotherapy for the treatment of higher stage disease.
What is the role of Immunotherapy in Colon Cancer?
Cancer cells utilize certain mechanisms to escape from the immune system of the patient from attacking these cells. Immunotherapeutic agents activate the immune system to recognize and kill cancer cells.
Immune checkpoint inhibitors target PD-1, a protein on T-cells that normally helps keep these cells from attacking cancer cells. This activates the immune system to kill the PD-L1 expressing cancer cells.
Pembrolizumab and nivolumab have been approved as the second- or third-line therapy for patients with unresectable or advanced/metastatic, dMMR/MSI-H positive colorectal cancers that have progressed on prior treatment (except a checkpoint inhibitor).
Best Colon Cancer Specialist in Delhi
Dr Sunny Garg is a renowned Medical Oncologist in New Delhi with an experience of more than 6 years of treating colon cancer patients. He has practiced in leading cancer hospitals in Delhi, and currently practicing at Manipal Hospital, Dwarka.
He has a vest experience of treating colon cancer patients in all stages of disease. He is well versed with Immunotherapy, Targeted therapy, and Chemotherapy for Colon Cancer treatment and also general supportive care for patients. He works in close collaboration with surgical and radiation oncologists, oncopathologists, nuclear medicine, and genetic counselors for comprehensive cancer care for the patients.
Call +91 9686813020 for appointment.