Treatment Options Update: Colorectal Cancer
Treatment for colorectal cancer often involves a combination of surgery and medication.
In approximately 80 percent of patients diagnosed with colorectal cancer, the cancer is localized (has not spread to other organs). Surgery is most often the first step in treating localized colorectal cancer. The surgeon will remove the section of the colon or rectum that contains the tumor and will also remove nearby lymph nodes, which are small organs located throughout the body that remove waste and fluids and help fight infection. Removing the colon or rectal tumor and nearby lymph nodes enables a pathologist (a physician who examines laboratory samples of body tissue for diagnostic purposes) to more accurately determine the stage of the cancer.
Chemotherapy is sometimes given before surgery to try to shrink the tumor (called “neoadjuvant” treatment), making the surgery an easier process and increasing its chances of success. Neoadjuvant chemotherapy is sometimes given in combination with radiation.
After surgery, cancer cells that are not detectable by tests may still exist, so doctors often suggest “adjuvant” treatment (chemotherapy given after surgery). The goal is to destroy any remaining tumor cells, decrease the chances of the cancer coming back and reduce the risk of tumor cells spreading to other parts of the body.
The chemotherapies most often given in adjuvant treatment are:
- 5-Fluorouracil (Adrucil),), also called 5-FU, is given intravenously (through a needle into a vein), often with the vitamin-like drug leucovorin (folinic acid) which helps it work more effectively.
- Capecitabine (Xeloda and others), taken in pill form, is changed by the body to 5-FU when it reaches the site of the tumor.
- Oxaliplatin (Eloxatin) is given intravenously in combination with 5-FU or capecitabine.
If the colorectal cancer has spread to other areas of the body, such as the liver or lungs, doctors often treat the tumor with chemotherapy alone. In addition to 5-FU and capecitabine, metastatic colorectal cancer can be treated with the intravenous drugs oxaliplatin (Eloxatin) and irinotecan (Camptosar).
In 2015, the FDA approved Lonsurf (a pill that combines two drugs, trifluridine and tipiracil) for people with advanced colorectal cancer which is no longer responding to other therapies.
Targeted therapies focus on specific molecules and cell mechanisms thought to be important for cancer cell survival and growth, taking advantage of what researchers have learned in recent years about how cancer cells grow. Targeted therapies are meant to spare healthy tissues and provide treatment against cancer cells that is more focused than chemotherapy.
- VEGF inhibitors. These treatments “starve” the tumor by blocking the action of VEGF (vascular endothelial growth factor), a protein released by tumors that contributes to blood vessel growth (angiogenesis). VEGF inhibitors bevacizumab (Avastin), ramucirumab (Cyramza) and ziv-aflibercept (Zaltrap) are given intravenously, typically along with chemotherapy such as oxaliplatin, irinotecan, 5-FU and capecitabine. VEGF inhibitors can help make chemotherapy drugs more effective.
- EGFR inhibitors. EGFR (epidermal growth factor receptor) is a protein often found in high amounts on the surface of cancer cells. The targeted therapies cetuximab (Erbitux) and panitumumab (Vectibix), given intravenously, are designed to block the action of EGFR, preventing cancer cells from growing into tumors. For patients with RAS wild-type tumors, they are often given in combination with chemotherapy.
- Kinase inhibitor. Kinase proteins send important signals to the cell’s control center, including signals that promote cell growth. The kinase inhibitor regorafenib (Stivarga), taken in pill form, is designed to help stop the growth of tumors by blocking several kinase proteins.
- TRK inhibitor. In November 2018, the FDA approved the TRK inhibitor larotrectinib (Vitrakvi) for the treatment of people with solid tumors (including colorectal cancer tumors) that have an NTRK gene fusion and have progressed following treatment or have no other satisfactory treatment alternative. Larotrectinib is “agnostic” in that it targets a genetic driver of cancer rather than a specific type of tumor.
Our immune system works constantly to keep us healthy. It recognizes and fights against danger, such as infections, viruses and growing cancer cells. In general terms, immunotherapy uses our own immune system as a treatment against cancer.
In 2017, the immunotherapy drugs pembrolizumab (Keytruda) and nivolumab (Opdivo), known as PD-1 inhibitors, were granted accelerated approval by the FDA for people with metastatic colorectal cancer that has progressed after chemotherapy and that has one of two specific genetic features (MSI-H or DNA mismatch repair deficiency), both of which can prevent DNA within cells from repairing itself.
In July 2018, the FDA approved nivolumab in combination with the immunotherapy ipilimumab (Yervoy) for the treatment of people with previously-treated metastatic colorectal cancer that is positive for either MSI-H or DNA mismatch repair deficiency.
Immunotherapy continues to be a key area of research in the treatment of metastatic colorectal cancer, including:
- Vaccines.Vaccines that boost the immune system have the potential to treat colorectal cancer or prevent it from recurring after treatment. A number of vaccines are being studied in clinical trials. One vaccine approach involves removing a person’s own immune system cells from their blood, altering them with a substance that will instruct them to attack cancer cells and injecting them back into the person’s body.
- Immune checkpoint inhibitors. Tumor cells often have “immune checkpoint” molecules that act as a shield, allowing the cancer to evade an attack by the immune system. This can be countered by immune checkpoint inhibitors, which are drugs designed to remove the shield and allow the immune system to attack the cancer cells.
- Combining immunotherapy and targeted therapy. PD-1 is a molecular “brake” that prevents the body’s immune system from attacking tumors. Combining PD-1 inhibitors with targeted or other therapies that activate immune cells may stimulate the immune system to attack cancer cells.
Personalizing Treatment: The Role of Genetic Mutations
Each tumor has its own biological makeup, based on the genes found in its cells. The genes in tumor cells are different from genes in healthy cells in the body. An important area of cancer research is understanding this biology. With this information, it’s possible for doctors to know whether a particular tumor is likely to respond to a specific treatment, allowing for the best possible treatment approach. This is known as precision (or personalized) medicine.
To better understand the biological makeup of a person’s tumor, doctors look for changes in genes within the tumor that may serve as “markers.” Markers can predict whether a given treatment will be effective against a tumor and whether there is a high risk of the tumor recurring (the cancer returning).
There are tumor markers and genetic changes that can be identified in colorectal cancer:
A key group of tumor markers that have been found in colorectal cancer consists of changes in KRAS and NRAS—known collectively as the RAS genes. Forty percent of people with colorectal cancer have a mutation (change) in a RAS gene. Through clinical trials, researchers have learned that these people do not benefit from treatment with the EGFR inhibitors cetuximab and panitumumab (see “Targeted Therapy” section). However, the presence of these
genetic alterations does not affect response to chemotherapy. The other 60 percent of people with colorectal cancer have no RAS mutation; these people are said to have the RAS “wild-type” gene. These individuals have a higher likelihood of benefiting from treatment with EGFR inhibitors.
As with RAS mutations, the majority of patients with mutations in the BRAF gene do not respond to EGFR inhibitors. Through clinical trials, doctors have learned there are certain drugs that may be able to block this BRAF gene, which may allow patients with this mutation to respond to treatment with EGFR inhibitors. This is an active area of research, and combination therapies that block the BRAF gene are now available.
About 4 percent of metastatic colorectal cancers (cancers that have spread to other parts of the body) have a genetic trait known as high microsatellite instability (MSI-H), which causes these tumors to have a large number of genetic mutations. Two drugs are approved by the U.S. Food and Drug Administration (FDA) for the treatment of this type of tumor (see “Immunotherapy” section) and additional treatment approaches are being studied in clinical trials.
A genetic abnormality can cause the neurotrophic receptor tyrosine kinase (NRTK) gene in a cancer cell to become connected (fused) to another unrelated gene. When this occurs, it causes uncontrolled “signaling” of tropomyosin receptor kinase (TRK) proteins that can lead to tumor growth. A TRK inhibitor was recently approved by the FDA for the treatment of people with colorectal cancer that exhibits this genetic abnormality (see “Targeted Therapy” section).
Information provided by CancerCare.
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