by Jason Wasserman MD PhD FRCPC
February 9, 2023
Adenoid cystic carcinoma (ACC) is a slow-growing but locally aggressive type of cancer most commonly found in the head and neck. Other possible locations include the skin, lungs, breasts, and prostate gland.
ACC grows slowly but spreads widely into surrounding tissues. However, unlike other types of cancer, ACC does not typically spread to lymph nodes unless it undergoes high-grade transformation (see below).
The symptoms of ACC depend on where the tumour starts and the size of the tumour. Symptoms associated with tumours in the head and neck include pain, numbness, and tingling in the area of the tumour. In the skin or breast, the tumour may appear as a painless lump or nodule. Tumours in the lung may cause shortness of breath, coughing, or wheezing.
At present, the causes of ACC remain unknown. However, approximately half of all tumours have a genetic alteration involving the genes MYB, MYBL1, or NFIB.
When examined under the microscope, ACC is made up of two types of cells: ductal cells and myoepithelial cells. As a result, ACC is sometimes described as a biphasic salivary gland tumour. The tumour cells in ACC commonly show two patterns of growth: tubular and cribriform. In the tubular pattern, the tumour cells connect together to create a ring-shaped structure with a hole in the centre. In the cribriform pattern, the tumour cells connect together to form makes small spaces called microcysts. These microcysts are often filled with blue or pink-coloured material.
High grade transformation in ACC means that the tumour has started to change in a way that results in more aggressive behaviour. When examined under the microscope, tumours with high grade transformation have lost some of the features typically seen in an ACC. In particular, the tumour cells often stick together to create large groups of cells without the microcysts typically seen in ACC. Pathologists use the term solid to describe this pattern of growth. Tumours with high grade transformation often have more mitotic figures (tumour cells dividing to create new tumour cells) and a type of cell death called necrosis may also be seen. High grade transformation is important because these tumours are more likely to metastasize (spread) to lymph nodes and the lungs.
Perineural invasion is a term pathologists use to describe cancer cells attached to or inside a nerve. A similar term, intraneural invasion, is used to describe cancer cells inside a nerve. Nerves are like long wires made up of groups of cells called neurons. 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 the cancer cells can use the nerve to spread into surrounding organs and tissues. This increases the risk that the tumour will regrow after surgery. Perineural invasion is almost always seen in an ACC.
Lymphovascular invasion means that cancer cells were seen inside 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. The lymphatic vessels connect with small immune organs called lymph nodes that are found throughout the body. 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.
In pathology, a margin is the edge of a tissue that is cut when removing a tumour from the body. The margins described in a pathology report are very important because they tell you if the entire tumour was removed or if some of the tumour was left behind. The margin status will determine what (if any) additional treatment you may require.
Most pathology reports only describe margins after a surgical procedure called an excision or resection has been performed for the purpose of removing the entire tumour. For this reason, margins are not usually described after a procedure called a biopsy is performed for the purpose of removing only part of the tumour. The number of margins described in a pathology report depends on the types of tissues removed and the location of the tumour. The size of the margin (the amount of normal tissue between the tumour and the cut edge) depends on the type of tumour being removed and the location of the tumour.
Pathologists carefully examine the margins to look for tumour cells at the cut edge of the tissue. If tumour cells are seen at the cut edge of the tissue, the margin will be described as positive. If no tumour cells are seen at the cut edge of the tissue, a margin will be described as negative. Even if all of the margins are negative, some pathology reports will also provide a measurement of the closest tumour cells to the cut edge of the tissue.
A positive (or very close) margin is important because it means that tumour cells may have been left behind in your body when the tumour was surgically removed. For this reason, patients who have a positive margin may be offered another surgery to remove the rest of the tumour or radiation therapy to the area of the body with the positive margin. The decision to offer additional treatment and the type of treatment options offered will depend on a variety of factors including the type of tumour removed and the area of the body involved. For example, additional treatment may not be necessary for a benign (non-cancerous) type of tumour but may be strongly advised for a malignant (cancerous) type of tumour such as ACC.
Lymph nodes are small immune organs found throughout the body. Cancer cells can spread from a tumour to lymph nodes through small vessels called lymphatics. For this reason, lymph nodes are commonly removed and examined under a microscope to look for cancer cells. The movement of cancer cells from the tumour to another part of the body such as a lymph node is called a metastasis.
Cancer cells typically spread first to lymph nodes close to the tumour although lymph nodes far away from the tumour can also be involved. For this reason, the first lymph nodes removed are usually close to the tumour. Lymph nodes further away from the tumour are only typically removed if they are enlarged and there is a high clinical suspicion that there may be cancer cells in the lymph node.
If any lymph nodes were removed from your body, they will be examined under the microscope by a pathologist and the results of this examination will be described in your report. Most reports will include the total number of lymph nodes examined, where in the body the lymph nodes were found, and the number (if any) that contain cancer cells. If cancer cells were seen in a lymph node, the size of the largest group of cancer cells (often described as “focus” or “deposit”) will also be included.
The examination of lymph nodes is important for two reasons. First, this information is used to determine the pathologic nodal stage (pN). Second, finding cancer cells in a lymph node increases the risk that cancer cells will be found in other parts of the body in the future. As a result, your doctor will use this information when deciding if additional treatment such as chemotherapy, radiation therapy, or immunotherapy is required.
Pathologists often use the term “positive” to describe a lymph node that contains cancer cells. For example, a lymph node that contains cancer cells may be called “positive for malignancy” or “positive for metastatic carcinoma”.
Pathologists often use the term “negative” to describe a lymph node that does not contain any cancer cells. For example, a lymph node that does not contain cancer cells may be called “negative for malignancy” or “negative for metastatic carcinoma”.