Low grade serous carcinoma of the ovary

What is low-grade serous carcinoma of the ovary?

Low-grade serous carcinoma is a type of ovarian cancer. It develops from the specialized epithelial cells on the outer surface of the ovary or the lining 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. If your pathologist also sees a serous borderline tumour, it will be described in the report.

The ovary

The ovaries are part of the female reproductive tract. They are small round organs that are connected to the uterus by the fallopian tubes. The outer surface of the ovaries and the inside of the fallopian tubes are lined by specialized cells called epithelial cells that form a barrier called the epithelium. The tissue below the epithelium is called the stroma.

How do pathologists make this diagnosis?

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.​

Tumour site

After carefully examining your tissue under the microscope, your pathologist will attempt to determine where the tumour started even if it has spread to multiple organs. The location where the tumour started is called the primary site. In some cases, the primary site can be determined and will be included in your report as ovary or peritoneum. In many cases, however, your pathologist will not be able to determine where the tumour started and the primary site will be described as ‘other’.

Intact or ruptured tumour

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 (see Pathologic stage below).

Cancer cells 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 (see Pathologic stage below).

Other organs or tissues involved

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 (see Pathologic stage below).​

Lymph nodes

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.

Lymph node

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 (see Pathologic stage below).

Normal lymphatics of pelvis

Pathologic stage

​The pathologic stage for low-grade serous carcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer. This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M)  to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and a worse prognosis.

Tumour stage (pT)
ovary cancer T1 T2 T3Nodal stage (pN)

Node stage ovary cancer

Metastatic stage (pM)

ovary cancer M stage

by Emily Goebel, MD FRCPC (updated September 1, 2021)
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