by Jason Wasserman MD PhD FRCPC
August 2, 2022
Micronodular basal cell carcinoma (BCC) is a type of skin cancer. The tumour is made up of specialized basal cells that are normally found in a part of the skin called the epidermis. This type of cancer is called “micronodular” because the tumour is made up of very small (“micro”) groups of cancer cells called nodules. The nodules of cancer cells typically spread deeply into a part of the skin called the dermis.
Like other types of BCC, micronodular BCC is associated with long-term excessive exposure to the sun or other sources of UV radiation (such as tanning beds). Severe sunburns, especially at a young age, increase the risk of developing basal cell carcinoma.
Micronodular BCC typically does not cause any symptoms but can be seen as a flat or raised growth with edges that blend into the surrounding normal skin.
Most micronodular BCCs are found on the head and neck. However, any sun-exposed area of skin can be affected.
The recommended treatment for micronodular BCC is surgically removing the entire tumour.
Micronodular BCC is considered a high-risk type of basal cell carcinoma because the cancer cells grow deep into the skin which makes it difficult for surgeons to fully remove the tumour. As a result, micronodular BCC is more likely to regrow after surgery compared to other low-risk types of BCC.
Like all types of BCC, micronodular BCC rarely spreads to other parts of the body such as lymph nodes or the lungs. However, the tumour can regrow after treatment, especially if the entire tumour is not completely removed.
Micronodular BCC starts in a layer of tissue at the surface of the skin called the epidermis. The layers below the epidermis are called the dermis and subcutaneous tissue. Pathologists use the term depth of invasion to describe how far the tumour cells have spread from the epidermis into the layers of tissue below (the dermis and subcutaneous tissue). The depth of invasion is important because tumours that grow deeper into the dermis are more likely to regrow after treatment. For skin tumours, the depth of invasion is measured from the surface of the skin to the deepest point of invasion. Some pathology reports describe the depth of invasion as tumour thickness.
Perineural invasion means that cancer cells were seen attached to a nerve. Nerves are found all over the body and they are responsible for sending information (such as temperature, pressure, and pain) between your body and your brain. Perineural invasion is important because cancer cells that have become attached to a nerve can spread into surrounding tissues by growing along the nerve. This increases the risk that the tumour will regrow after treatment. Micronodular BCC is more likely than other types of BCC to show perineural invasion.
Lymphovascular invasion means that cancer cells were seen inside of a blood vessel or lymphatic vessel. Blood vessels are long thin tubes that carry blood around the body. Lymphatic vessels are similar to small blood vessels except that they carry a fluid called lymph instead of blood. Lymphovascular invasion is important because cancer cells can use blood vessels or lymphatic vessels to spread to other parts of the body such as lymph nodes or the lungs. Micronodular BCC very rarely shows lymphovascular invasion. However, when found it is associated with a higher risk that the cancer cells will spread to lymph nodes.
A margin is a rim of normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. The margins are usually only described in a pathology report after an excision has been performed to remove the tumour. Margins are often not described after a biopsy.
When examining micronodular BCC under the microscope, a margin is considered positive when there is no distance between the cancer cells and the cut edge of the tissue. A margin is called negative when there are no cancer cells at the cut edge of the tissue. A positive margin is associated with a higher risk that the tumour will regrow in the same site after treatment.