by Emily Goebel, MD FRCPC
October 7, 2022

What is low-grade serous carcinoma of the ovary?

Low-grade serous carcinoma is a type of ovarian cancer. It develops from cells normally found on the outside surface of the ovary or the tissue that lines the inside of the abdominal cavity. It is an uncommon, slow-growing cancer that usually has spread to other organs including the fallopian tube and uterus by the time it is diagnosed. In some cases, low-grade serous carcinoma develops from a non-cancerous type of tumour called a serous borderline tumour.

What are the symptoms of a low-grade serous carcinoma?

Small tumours usually do not cause any symptoms and are only found incidentally when imaging is performed for another reason. Large tumours may cause symptoms such as abdominal pressure, pain, or bloating.

What causes low-grade serous carcinoma?

At present doctors do not know what causes low-grade serous carcinoma.

How is this diagnosis made?

The diagnosis of low-grade serous carcinoma can also be made after a small sample of tissue is removed in a procedure called a biopsy. In this procedure, a small sample of tissue from the pelvis or abdomen is removed. The ovary itself is not usually biopsied.

For some women, the diagnosis of low-grade serous carcinoma is only made when the entire tumour has been surgically removed and sent to a pathologist for examination. Other organs such as the fallopian tube and uterus may be removed at the same time as the ovary.

Your surgeon may request an intraoperative or frozen section consultation from your pathologist. The diagnosis made by your pathologist during the intraoperative consultation can change the type of surgery performed or the treatment offered after the surgery is completed.​

Why is it important if the tumour was received intact or ruptured?

All ovarian tumours are examined to see if there are any holes or tears in the outer surface of the tumour or ovary. The outer surface is referred to as the capsule. The capsule is described as intact if no holes or tears are identified. The capsule is described as ruptured if the outer surface contains any large holes or tears. This information is important because a capsule that ruptures inside the body may spill cancer cells into the abdominal cavity. A ruptured capsule is associated with a worse prognosis and is used to determine the tumour stage.

Were cancer cells seen on the surface of the ovary or fallopian tube?

The cancer cells in low-grade serous carcinoma can spread from the ovary to another nearby organ such as the fallopian tube or the ovary on the other side of the body. If cancer cells are seen on the surface of the fallopian tube or ovary, it suggests that they have spread there from another site. This information is important because a tumour that has spread from one organ to another is given a higher tumour stage.

Has the tumour spread to other organs or tissues in the pelvis or abdomen?

Small samples of tissue are commonly removed in a procedure called a biopsy to see if cancer cells have spread to the pelvis or abdomen. These biopsies which are often called omentum or peritoneum are sent for pathological examination along with the tumour.

Other organs (such as the bladder, small intestine, or large intestine) are not typically removed and sent for pathological examination unless they are directly attached to the tumour. In these cases, your pathologist will examine each organ under the microscope to see if there are any cancer cells attached to those organs. Cancer cells in other organs are used to determine the tumour stage.​

Were lymph nodes examined and did any contain cancer cells?

Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour. The movement of cancer cells from the tumour to a lymph node is called metastasis.

Your pathologist will carefully examine all lymph nodes for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells.

If cancer cells are found in a lymph node, the size of the area involved by cancer will be measured and described in your report.​

• Isolated tumour cells – The area inside the lymph node with cancer cells is less than 0.2 millimetres in size.
• Micrometastases – The area inside the lymph node with cancer cells is more than 0.2 millimetres but less than 2 millimetres in size.
• Macrometastases – The area inside the lymph node with cancer cells is more than 2 millimetres in size.

Cancer cells found in a lymph node are associated with a higher risk that the cancer cells will be found in other lymph nodes or in a distant organ such as the lungs. The number of lymph nodes with cancer cells is also used to determine the nodal stage.