Skin cancer sometimes spreads to other areas of the body, often the lymph nodes. Your lymph nodes are located throughout your body and work to fight infection and filter out toxins from the bloodstream but sometimes cancer cells begin growing in the lymph nodes.
When skin cancer is diagnosed, your doctor may recommend testing to determine whether your lymph nodes are affected. This is done through a biopsy or diagnostic tools such as a CT scan. If the cancer has spread to the lymph nodes, your doctor may recommend a lymph node dissection.
During a lymph node dissection, your doctor removes the lymph nodes closest to the primary cancer site - for example, if skin cancer is detected on your arm, the lymph nodes in your armpit on the side of your body the cancer is found will be removed. Lymph nodes are not removed individually, instead an area of tissue surrounding the lymph nodes is removed. Once removed, a pathologist examines the tissue, looks for cancer cells and counts the lymph nodes.
Axillary Lymph Node Dissection
Each axilla, or armpit, has lymph nodes. When removing these, some of the tissue around your chest wall muscle is also removed.
Inguinal Lymph Node Dissection
There are also lymph nodes in your groin area. When these are removed, the doctor may need to move a muscle in your outer thigh to help protect the area dissected.
Side Effects of Lymph Node Dissection
One of the most common side effects of a lymph node dissection is lymphedema. This causes swelling, pain or discomfort in the entire limb. The lymph nodes helps to drain fluid from the limbs and once removed, that fluid can build up. The swelling may or may not go away and, when severe, can increase your risk of infection. Some find that using stockings or compression sleeves can help to reduce the swelling. Your doctor will discuss post-operative care that reduces your chances of developing lymphedema.
Another possible side effect is numbness in the limb. Because there are nerves in the tissue removed during a lymph node dissection, you may feel some numbness in your limb. You should not experience any affect on your use of the limb or in strength.
As with any surgery, you will need to take special care of the area, should limit your movement of the limb and monitor the area for any signs of infection.
You may also need to have a drain placed in your limb. A small plastic tube is inserted into your skin and attached to a bulb to collect drainage. This is often left in place for a few weeks after your surgery. Once the drainage stops, your doctor will remove the plastic tube.
Deciding on Lymph Node Dissection
When lymph nodes are removed, a pathologist examines them to determine the stage of cancer and this information can help you and your doctor determine the best course of treatment. However, a lymph node dissection also has the potential to cause serious side effects, which may or may not go away. Swelling from lymphedema, an increased risk of infection and numbness may continue for long after the surgery.
Whether lymph node dissection is needed is still being debated. According to the American Cancer Society, "It is not clear if a lymph node dissection can cure melanomas that have spread to the nodes. This is still being studied."  However, "Some doctors feel it might prolong a patient’s survival and at least avoid the pain that may be caused by cancer growing in these lymph nodes." 
There are risks and potential benefits to having a lymph node dissection. Make sure to talk with your doctor about the pros and cons. Ask why he believes this is the best choice for you. Once you have all the information, you can make an informed decision about what is best in your situation.
"Lymph Node Involvement," Date Unknown, Staff Writer, Skin Cancer Foundation
  "Surgery for Melanoma Skin Cancer," Revised 2013, May 30, Staff Writer, American Cancer Society
"Treatment of Melanoma Skin Cancer by Stage," Revised 2013, May 30, Staff Writer, American Cancer Society