What is Radiation Therapy for Anal Cancer?
Anal cancer is quite rare, making up about 10% of all anorectal cancers, although the number of cases has been rising over the past several decades. In the past, the usual treatment was a type of surgery called abdominoperineal resection (APR), but nowadays, doctors often use a combination of chemotherapy and radiation to preserve the organ.
Understanding the anatomy of the anal canal can be helpful in learning about anal cancer. The anal canal extends from the anal verge, which is where the internal anal canal meets the external anal skin (covered with hair), to the anorectal ring, which is where the rectum joins a muscle sling called the puborectalis. The anal canal is usually 3 to 5 cm long.
The dentate line is the boundary inside the anal canal where the type of tissue changes. Above this line, the tissue is columnar mucosa, similar to what you find in the colon. Below this line, the tissue is squamous epithelium, which is a more common tissue type found in the body.
The anal margin, also known as perianal skin, is a ring of tissue around the anus that extends 5 cm outward. The type of tissue found here is squamous epithelium.
The way anal cancer spreads, or how its lymphatic drainage works, depends on where the cancer is located concerning the dentate line. Cancers above the dentate line spread to the nodes around the sacrum and internal iliac nodes. Cancers below the dentate line spread to the nodes in the upper thigh and femoral nodes.
What Causes Radiation Therapy for Anal Cancer?
High-grade anal intraepithelial neoplasia, or AIN, is a condition that can develop into anal cancer if not treated. It’s typically caused by infection with human papillomavirus (HPV), especially types 16 and 18. HPV is usually spread through direct skin contact and sex.
Some factors could increase your risk of getting anal cancer. These include having HIV, having many sexual partners, smoking, having a weak immune system for reasons other than HIV, and certain chronic inflammation conditions like Crohn disease.
On a more positive note, there are preventative vaccines for HPV. Getting these vaccines before exposure to HPV can lower the rates of AIN. They should be considered especially for people who are at a higher risk for anal cancer.
Risk Factors and Frequency for Radiation Therapy for Anal Cancer
Anal canal cancer rates have been on the rise over recent years, particularly amongst women. As of now, this disease accounts for 0.5% of all cancer diagnoses in the United States. Back in 2018, there were roughly 8,580 cases recorded per year in the US, with women having 5,620 of these cases and men having 2,960. This disease also led to around 1,160 deaths annually, with women accounting for 680 deaths and men 480. This type of cancer most often affects older adults, with the average patient being in their early 60s. Nevertheless, individuals who are HIV-positive often experience the onset of this disease at an earlier age.
- Anal canal cancer rates are increasing, especially among women.
- It represents 0.5% of all cancer diagnoses in the United States.
- In 2018, it was estimated that there were approximately 8,580 cases per year in the US (5,620 in women and 2,960 in men).
- The disease also caused around 1,160 yearly deaths in the US (680 in women and 480 in men).
- The average age of patients suffering from this cancer is usually in their early 60s.
- HIV-positive patients tend to experience the onset of the disease earlier.
Signs and Symptoms of Radiation Therapy for Anal Cancer
Anal cancer may present with various symptoms. Some people might bleed (in about 45% of cases) or experience pain (about 30% of cases). Others symptoms could include itching, noticing a mass around the anus, feeling an urgent need to defecate, or seeing a change in the size or shape of their stool. More advanced cases might also involve symptoms like mucus discharge, swelling in the lower legs, or sores around the anus that don’t heal. Interestingly, early-stage anal cancer might not cause any noticeable symptoms at all and can sometimes be discovered by accident during a routine exam or specific tests like anoscopy or proctoscopy. Note that a colonoscopy might miss an anal tumor because it can be difficult to angle the scope into the anal canal. Less than 10% of people with squamous cell anal cancer have cancer that has spread to other parts of the body when they’re diagnosed. The most common places for the cancer to spread are the liver and the lungs, and the symptoms related to this spread will depend on where the cancer has moved and how much cancer is present.
- Bleeding (45% of cases)
- Pain (30% of cases)
- Itching
- Perianal mass
- Fecal urgency
- Change in stool caliber
- Mucus discharge (in advanced cases)
- Lower extremity edema (in advanced cases)
- Non-healing perianal wounds (in advanced cases)
Testing for Radiation Therapy for Anal Cancer
After confirming a diagnosis of squamous cell carcinoma of the anal canal through a tissue sample, a series of additional tests are recommended. These tests include a physical examination of the rectum by inserting a gloved finger (DRE), checking for lymph nodes in the groin area and taking tissue samples of any suspicious ones. Doctors also recommend chest and abdominal CT scans, as well as pelvic CT or MRI images to look for any signs of the disease spreading.
In addition, an anoscopy (a procedure to look inside the anus), a complete blood count (CBC) test, a comprehensive metabolic panel (CMP) test, and HIV testing (if HIV status is unknown) are also suggested. For women, a gynecological exam too is recommended, including screening for cervical cancer as per the National Comprehensive Cancer Network (NCCN) guidelines.
A PET/CT is another useful test to plan radiation treatment and to check for the spread of cancer cells in the body. This test can accurately find and measure lymph nodes in the groin area with a sensitivity of 93% (detecting when disease is present) and specificity of 76% (detecting when disease is absent).
Doctors might also carry out a sentinel lymph node biopsy, a test which identifies the first few lymph nodes into which a tumor drains. This test could be beneficial in evaluating the lymph nodes in the groin.
Treatment Options for Radiation Therapy for Anal Cancer
Cancers located at the outer edge of the anus (anal margin cancers) are often detected in the early stages, and as a result, they tend to have a better prognosis, or outcome. These types of cancers are typically managed similarly to skin cancer – either by surgically removing a significant portion of the affected area, or with radiotherapy alone, which is a treatment using high energy beams to destroy cancer cells. For more severe cases of anal margin cancer, the treatment approach becomes similar to how cancers in the anal canal are treated.
Previously, the common way to manage tumors in the anal canal was through a surgery called abdominoperineal resection, which involves removing the anus, rectum, and part of the colon, necessitating a permanent colostomy – an artificial opening in the abdominal wall for waste removal. However, since the 1980s, these surgeries have been largely replaced by a combination of chemotherapy and radiation, in order to preserve the anus. This combined treatment has shown equal survival rates and better rates of avoiding colostomies, making it the preferred treatment option. The radiation used in this process is usually intensity-modulated radiation therapy, which can be specifically targeted to the tumor. Chemotherapy is commonly administered alongside and tends to be a combination of different cancer-fighting drugs.
When deciding on the appropriate treatment, the overall health and well-being of the patient is a critical consideration. If patients are in poor health, they may not be able to withstand the combined chemotherapy and radiation treatment. In these cases, or in cases where patients already have bowel issues or a fistula (an abnormal connection between two body parts), surgical treatment may be more appropriate.
Patients living with HIV/AIDS have a significantly higher incidence of anal cancer. While they may face higher rates of local relapses and more severe skin reactions to treatment, there don’t appear to be notable differences in the rates of complete response to treatment or 5-year survival rates. Throughout treatment, they should continue taking their antiretroviral therapy to manage their HIV. Their CD4 count, a measure of their immune system’s health, should also be monitored and chemotherapy can be adjusted to avoid complications. Though there may be some concerns around increased blood-related toxicities, the standard chemotherapy regimen remains the most effective. In patients with uncontrolled HIV and low CD4 count or high viral loads, a different chemotherapy regimen may be used to minimize risk.
What else can Radiation Therapy for Anal Cancer be?
The possible conditions that could be mistaken for anal cancer depend on the symptoms a patient presents. For instance, noticeable bright red blood in the stool could be not only a sign of anal cancer, but might also be caused by:
- Hemorrhoids
- Polyps in the bowel
- Diverticulosis, small, bulging pouches forming in the digestive system
- Fissures, small tears in the anus
- Ulcers
- Abscesses
- Proctitis, inflammation of the lining of the rectum
A large malignant tumor at the end of the bowel could also come from the rectum, bladder, prostate or vagina.
Surgical Treatment of Radiation Therapy for Anal Cancer
In the past, the standard treatment for anal cancers was a procedure called the Abdominoperineal Resection (APR), which involved the surgical removal of the lower part of the colon, rectum, and anal sphincter complex. This procedure was performed using both abdominal and perineal (the area between the genitals and the anus) incisions. However, APR often required patients to have a permanent colostomy (a surgical procedure where an opening is created in the abdominal wall to allow waste from the body to bypass the normal route). Additionally, APR’s effectiveness was limited, with only a 50% survival rate over 5 years and a 30% chance of the cancer recurring.
In order to improve these outcomes, improved methods involving chemotherapy and radiation were developed. The success of these treatments in early studies, where 80% of patients showed complete recovery, led to these methods being used as the initial treatment for anal cancer. As a result, APR is nowadays used primarily as a fallback option for treatment, or for patients whose anal sphincters are non-functional at diagnosis. Treatment for Adenocarcinomas, a type of anal canal cancer, might also involve preserving the organ.
Another option could be a local excision in patients with a specific type of anal canal cancers (T1N0M0), assuming sphincter function can be maintained. This procedure involves removing the cancer with a safe margin of healthy tissue. However, the cure rates for local excision are quite low, around 60% at 5 years, with a high local recurrence rate of 40%. Therefore, local excision is usually reserved for special cases, such as a patient who is not healthy enough for more intensive treatments.
What to expect with Radiation Therapy for Anal Cancer
A large main tumor, having cancer spread to lymph nodes or other parts of the body (metastases), being male, and an HIV-positive status all make the prognosis worse. When patients have a tumor initially measuring more than 5 cm, they have a higher risk of needing a surgery called a colostomy. Most patients (50 to 60 percent) have smaller lesions less than 5 cm, tied with a survival rate over 5 years of 80 to 90 percent. The rate of cancer spread to lymph nodes varies depending on the cancer stage. It can range from 10 to 60 percent, which brings down the 5-year survival rate to 60 percent. The 5-year survival rates for different stages of squamous cell cancer of the anus were found to be 77% for stage I, 67% for stage II, 58% for stage IIIA, 51% for stage IIIB, and 15% for stage IV.
In terms of monitoring after initial treatment, the doctors will do a digital rectal exam (DRE) around 2 to 3 months after the chemoradiation course is finished. Following this, patients are categorized based on their response to the treatment as either complete response, partial response, or progressive disease. If the disease is still there but hasn’t worsened, the patient will be closely monitored to see if further reduction in the disease occurs. Some patients see the disease continue to lessen even 6 months after starting treatment, allowing them to avoid a major surgery called an abdominoperineal resection (APR). If biopsy results after 26 weeks show the disease or if the disease worsens at any point, more intense treatment is then pursued. Despite the lack of solid proof to promote using PET/CT scanner to assess how the body responds to treatment regularly, a complete response on a PET/CT scan is linked to better survival chances and longer periods without the disease advancing.
Possible Complications When Diagnosed with Radiation Therapy for Anal Cancer
Patients treated with Intensity-Modulated Radiation Therapy (IMRT) usually experience fewer long-term side effects compared to those treated with traditional radiation techniques. Approximately 20% of these patients experience severe, acute non-blood related side effects. These can include skin peeling, inflammation of the rectum and bladder, and diarrhea.
About 60% of patients can have severe, acute blood-related side effects, most commonly a reduction in neutrophils, a type of white blood cell. The most frequent late side effect is mild diarrhea in about 35% of patients—however, this is usually manageable with standard treatments.
Some other long-lasting side effects of chemoradiation could include continuous inflammation of the rectum, abnormal blood vessels, and less often, hip fractures, abnormal connections between organs, sexual dysfunction, or narrowings.
Common Side Effects:
- Skin peeling
- Inflammation of the rectum and bladder
- Diarrhea
- Reduction in neutrophils
Late Side Effects:
- Mild diarrhea
- Continuous inflammation of the rectum
- Abnormal blood vessels
- Hip fractures
- Abnormal connections between organs
- Sexual dysfunction
- Narrowings
Preventing Radiation Therapy for Anal Cancer
People who are at a higher risk for developing anal cancer should be educated about the signs, symptoms, and risk factors associated with this disease. This includes people living with HIV, those who have multiple sexual partners, individuals with long-term immune system suppression not caused by HIV, and those with long-standing inflammatory conditions such as Crohn’s disease. Vaccines that protect against the Human Papillomavirus (HPV) could lower the risk of getting anal cancer. It is particularly important that these vaccines are given before exposure to the virus occurs. They should be more commonly used, especially among those who are at a high risk of contracting the disease.
