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# Low-grade serous ovarian tumours

- Lesion

Serous tumours that grow slowly: from a harmless cyst to a borderline tumour and, rarely, a low-grade cancer, driven by KRAS or BRAF rather than TP53.

Updated Nov 12, 2026

## Key points

- Cystadenoma: smooth-walled, usually unilocular cyst with clear fluid, lined by ciliated tubal-type cells.
- Borderline tumour: hierarchical branching papillae with tufting and mild to moderate atypia, but no destructive stromal invasion; often bilateral; excellent survival.
- Peritoneal implants of borderline tumours are usually noninvasive; invasive implants count as low-grade serous carcinoma.
- Low-grade serous carcinoma: small papillae and nests infiltrating stroma, uniform nuclei, many psammoma bodies; KRAS or BRAF, TP53 wild type.
- Psammoma bodies: laminated dystrophic calcifications, typical of papillary serous tumours.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Low-grade vs high-grade serous carcinoma
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes

- Study Test yourself

- Connections Connections

## What it is

Serous tumours are built of cells like those lining the fallopian tube. On the low-grade pathway, a benign serous cystadenoma or cystadenofibroma can give rise to a serous borderline tumour, which proliferates in branching papillae without invading, and some borderline tumours progress to low-grade serous carcinoma. These tumours carry KRAS, BRAF or ERBB2 mutations, keep wild-type TP53, grow slowly and respond poorly to chemotherapy. They are a different disease from high-grade serous carcinoma.

## Structure

- Benign: thin fibrous wall, a single layer of columnar ciliated cells, sometimes a fibrous stromal component (cystadenofibroma).
- Borderline: papillary excrescences on the inner or outer surface of the cyst; layered cells budding off in tufts.
- Micropapillary variant of borderline tumour: long slender papillae without branching, closer to carcinoma.
- Low-grade carcinoma: invasive small nests and micropapillae in retraction spaces, low mitotic rate.

## Step by step

- Tubal-type epithelium on the ovarian surface or in cortical inclusion cysts forms a benign serous cyst.
- A KRAS, BRAF or ERBB2 mutation lets a clone proliferate into papillae (borderline tumour).
- Additional changes in a minority allow destructive invasion (low-grade serous carcinoma).
- Spread is mostly along peritoneal surfaces; growth is slow over years.

## Low-grade vs high-grade serous carcinoma

| Feature | Low-grade serous carcinoma | High-grade serous carcinoma |
| --- | --- | --- |
| Precursor | Cystadenoma and borderline tumour | Serous tubal intraepithelial carcinoma |
| Key genes | KRAS, BRAF, ERBB2; TP53 normal | TP53 in nearly all; BRCA1 or BRCA2 in a share |
| Nuclei | Uniform, mild atypia | Marked atypia, many mitoses |
| Age and course | Younger, slow growth | Older, rapid spread |
| Chemotherapy | Responds poorly | Responds initially, often relapses |

## Markers

- PAX8 and WT1 positive
- p53 wild-type pattern
- Psammoma bodies (calcification)

## Clinical notes

- Present as an adnexal mass or are found on imaging; borderline tumours occur in younger women and can be treated with fertility-sparing surgery.
- CA-125 may be raised but is not specific.

## Memory aid

Low-grade serous goes slowly with KRAS and BRAF in the driver's seat; p53 is still on duty.

## Test yourself

Think of the answer, then tap the question to see it.

## What separates a serous borderline tumour from carcinoma?

The absence of destructive stromal invasion despite papillary proliferation and atypia.

## Which genes drive low-grade serous tumours?

KRAS, BRAF or ERBB2, with wild-type TP53.

## What is a psammoma body?

A laminated concretion of dystrophic calcium, typical of papillary tumours such as serous ovarian tumours.

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## Elsewhere in DurgiPedia

- [CA-125](https://durgical.com/en/biochemistry/topics/ca-125/)
- [Ovary: follicles, ovulation and corpus luteum](https://durgical.com/en/histology/ovary-follicles-ovulation-and-corpus-luteum/)

## Connections

## Related 6

- [High-grade serous carcinoma](https://durgical.com/en/general-pathology/high-grade-serous-carcinoma/)
- [Ovarian tumours: classification](https://durgical.com/en/general-pathology/ovarian-tumours-classification/)
- [Mucinous ovarian tumours](https://durgical.com/en/general-pathology/mucinous-ovarian-tumours/)
- [Benign vs malignant tumours: the comparison table](https://durgical.com/en/general-pathology/benign-vs-malignant-tumours-the-comparison-table/)
- [Pathologic calcification: dystrophic vs metastatic](https://durgical.com/en/general-pathology/pathologic-calcification-dystrophic-vs-metastatic/)
- [Oncogenes: RAS, MYC, HER2, BCR-ABL and the table to know](https://durgical.com/en/general-pathology/oncogenes-ras-myc-her2-bcr-abl-and-the-table-to-know/)

## Related conditions 3

- [Ovarian cancer](https://durgical.com/en/conditions/ovarian-cancer/)
- [Ovarian cyst](https://durgical.com/en/conditions/ovarian-cyst/)
- [Ovarian torsion](https://durgical.com/en/conditions/ovarian-torsion/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Epithelial Ovarian Cancer](https://www.ncbi.nlm.nih.gov/books/NBK567760/) (StatPearls (NCBI Bookshelf), 2026); [Ovarian Epithelial, Fallopian Tube, and Primary Peritoneal Cancer Treatment (PDQ®)–Health Professional Version](https://www.cancer.gov/types/ovarian/hp/ovarian-epithelial-treatment-pdq) (National Cancer Institute, 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/low-grade-serous-ovarian-tumours/