Ovary and fallopian tube -

Low grade serous carcinoma

This article was last reviewed and updated on November 19, 2018
by Emily Goebel, MD FRCPC

Quick facts:

  • Low grade serous carcinoma is a type of ovarian cancer.

  • The tumour can also start in the abdominal cavity from the thin layer of tissue that lines the abdominal organs.

  • Low grade serous carcinoma is an uncommon and slow growing tumour.

The normal ovary

The ovaries are part of the female reproductive tract. They are small organs that are attached to the uterus by the fallopian tubes. The outer surface of the ovaries are lined by a thin layer of specialized tissue called an epithelium that forms a barrier around the outside of the ovary. The epithelium is made up of specialized cells called epithelial cells.


The organs inside the abdomen are lined by a thin layer of tissue called the peritoneum that is made up of similar cells. The ovaries also contain large cells called eggs. The tissue below the epithelium is called stroma.

What is low grade serous carcinoma?

Low grade serous carcinoma is a type of ovarian cancer. It develops from the epithelial cells on the outer surface of the ovary or the lining of the abdominal cavity.


Regardless of where the tumour starts, it can spread to involve the ovaries, fallopian tubes, and peritoneal lining at the time of diagnosis. It is an uncommon, slow growing cancer that usually has spread to many organs by the time it is diagnosed.


In some cases, this cancer 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.

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. 


In some cases, the surgeon will 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’.

Tumour 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.

Why is this important? 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 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 traveled there from another site.


Why is this important? 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 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.

Why is this important? 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 (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called a 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 with cancer cells is less than 0.2 millimeters in size.

  • Micrometastases - The area inside the lymph node with with cancer cells is more than 0.2 millimeters but less than 2 millimeters in size.

  • Macrometastases - The area inside the lymph node with with cancer cells is more than 2 millimeters in size.

Why is this important? Cancer cells found in a lymph node is 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).

Treatment effect

If you were treated with chemotherapy (or other drugs designed to kill cancer cells) prior to surgical removal of your tumour, your pathologist will examine the tumour to determine the percentage of the tumour that is still alive (viable). The response will be categorized as follows:

  1. No/minimal response - Most of the tumour is alive.

  2. Appreciable response - Some of the tumour is dead and some is alive.

  3. Complete response - Almost all or all of the tumour is dead.

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 worse prognosis.


Pathologic stage is not reported on a biopsy specimen. It is only reported when the entire tumour has been removed in an excision or resection specimen.


Tumour stage (pT)

  • T0 - After careful examination of the tissue, no primary tumour is found. This can happen if you received treatment (for example chemotherapy) before surgery and the tumour shows complete response (see Treatment effect above).

  • T1a - The tumour is found only in one ovary or fallopian tube.

  • T1b - The tumour is found in both ovaries or fallopian tubes.

  • T1c - The tumour is found in only one ovary or fallopian tube but the tumour capsule is broken OR cancer cells were found in fluid taken out of the abdomen or pelvis.

  • T2a - The tumour extends to the uterus or cancer cells were found on the surface of the ovaries, fallopian tubes, or uterus (implants).

  • T2b - The tumour extends to other parts of the pelvis or cancer cells were found on the surface of tissues in the pelvis (implants).

  • T3 - Cancer cells are found outside of the pelvis in the tissues of the abdomen.

Nodal stage (pN)

  • NX - No lymph nodes were sent to pathology for examination.

  • N0 - No cancer cells are found in any of the lymph nodes examined.

  • N0(i+) -Only isolated cancer cells are found in a lymph node (see Lymph nodes above).

  • N1a - Cancer cells are found in a lymph node but the area with cancer cells is not greater than 10 millimeters.

  • N1b - Cancer cells are found in a lymph node and the area with cancer cells is greater than 10 millimeters.

Metastatic stage (pM)

Low grade serous carcinoma is given a metastatic stage between 0 and 1 based on the presence of tumour cells at a distant site in the body (for example the lungs). The metastatic stage can only be determined if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as MX.

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