Anal cancer is a rare disease and the understanding of its natural history is evolving. While it is the 26th most common cancer in the USA annually, the incidence rate is increasing at 2% per year over the past decade. Further underpinning its importance in recent times is that it is also one of the cancers that has devastatingly poor outcomes in the late stage while being relatively easy to detect and treat in the early stages.
What is Anal Cancer?
Anal cancer like all cancers start when the cells lose the ability to maintain their original form. Precancerous changes such as aberrant growth soon occurs as these cells no longer serve their original function and a tumor develops.
The anal canal is a 4 cm structure that continues from the rectum. Embryologically, this canal develops from 2 distinct stem cells that originate from different parts of the body. As the embryo develops into a fetus, these 2 stems cells develop into either Squamous Cells (outside of canal) or Columnar Cells (inside of anal canal). These 2 cells meet and develop into the anal canal. This is important because the junction at which these 2 cells converge while forming your anal canal all those years ago is also the most susceptible site for developing anal cancer.
Although not entirely analogous, anal cancer shares many similarities with cervical cancer in women. Both cancers occur most frequently at the junction where 2 normally distinct cells meet and majority of both tumors are found to be co-infected with Human Papilloma Virus (HPV) sub-type 16.
Men who have sex with Men (MSM) and immuncompromised patients (transplant, cancer patients and HIV patients) are more prone to this cancer. Compared to the general population, MSM with no HIV have 2 times the risk of developing anal cancer, MSM with HIV have up to 25 times the risk while transplant patients have 5 times the risk and a patient with previous colon cancer has 20 times the risk. Other risk factors include previous ano-genital warts, previous STD infection and high risk sexual activity.
Anal Cancer In The Early Stages
In its early stages, anal cancer does not produce any symptoms. The early signs of of developing anal cancer is pre-cancerous cell changes. This is detected by direct visualization and sampling of the area. The core principle of screening for anal cancer is hence looking for these pre-cancerous changes. This can be done through a variety of methods depending on the expertise available, each method has different levels of specificity in detecting anal cancer.
Anal Pap Smear & HPV Testing
Currently, the Anal PAP smear and HPV testing is considered to be the most practical means of screening for anal cancer. This involves a swab inserted into the anal canal and cells from the area are sampled and looked under a microscope for any pre-cancerous changes, further processing of the sample via HPV DNA PCR is also used to detect any presence of HPV in these cells. Once the patients with potential risk of developing anal cancers are pick out with this screening, a further diagnostic test is required. The current diagnostic standard is High Resolution Anoscopy where a high magnification scope is used to examine the tissue. Different reagents are also used to differentiate normal tissue from pre-cancerous tissue.
There are no established guidelines for how frequent screening should be carried out but current expert opinions recommend every 1 – 2 years for MSM with HIV and 2 – 3 years for MSM without HIV.
Treatment of Anal Cancer
Treatment of anal cancer can be considered in 2 categories – Pre-cancerous treatment and Cancer treatment. Precancerous changes, once detected by screening and diagnosed with Anoscopy can be treated with either Topical Therapy such to eradicate the precancerous tissues. Local Ablative Therapy that involves Radiofrequency Ablation can also be used to destroy the any precancerous tissue. Cancer treatment for pre-cancerous changes that have progressed to cancer, on the other hand requires surgery.
In both situations, close monitoring post treatment is essential as the recurrence rates are significant especially in high grade pre-cancerous changes.
Preventing pre-cancerous changes is essential to the approach of reducing anal cancer rates. HPV vaccination is shown to reduce pre-cancerous changes with a recent study showing 75% reduction in both Low and High grade changes in MSM population. There is also data suggesting that vaccination after precancerous changes have been detected is also able to reduce the rate of recurrence by approximately 20%.
In summary, anal cancer is disease in which majority of the tumors are driven by the HPV virus and in which pre-cancerous changes in the patients can accurately predict the chances of developing cancer especially in high risk populations. This makes screening and detection of early disease together with vaccination essential to reducing the rates of anal cancer.
Next read: PENILE CANCER – 7 THINGS YOU NEED TO KNOW!