Serous Ovarian Tumours and Psammoma Bodies
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Direct answer
Serous ovarian tumours are the commonest epithelial ovarian tumours and form a spectrum from benign serous cystadenoma through serous borderline tumour to low-grade and high-grade serous carcinoma. Psammoma bodies, which are concentric calcified spherules, are a classic histological finding. Bilateral involvement is more typical of malignant serous tumours than of benign ones.
What you must remember
- Benign: Serous cystadenoma is a cyst lined by a single layer of tubal-type ciliated epithelium, with no papillary growth or stromal invasion.
- Borderline: Serous borderline tumour shows epithelial proliferation and atypia without stromal invasion, and it has a good prognosis.
- Low grade: Low-grade serous carcinoma grows slowly, is linked to KRAS or BRAF mutations and responds less well to chemotherapy.
- High grade: High-grade serous carcinoma is the commonest ovarian cancer subtype and is associated with TP53 mutation in most cases.
- Psammoma bodies: Concentric laminated calcified spherules support a serous origin but do not by themselves define malignancy.
- Bilaterality: Bilateral disease is more common in malignant serous tumours and raises suspicion of cancer.
- Proposed origin: High-grade serous carcinoma is thought to arise from the fallopian tube through serous tubal intraepithelial carcinoma.
- Germline link: BRCA1 and BRCA2 mutations are strongly associated with high-grade serous carcinoma.
A sorting pathway from benign cyst to carcinoma
A serous tumour is sorted by a fixed set of histological questions, asked in order. Each answer narrows the diagnosis before grade and stage are considered.
- Check the lining: Benign cystadenomas have a smooth, single-layered lining with no papillary projections. Any papillary growth must be assessed further before the lesion is called benign.
- Look for atypia and papillae: Borderline tumours show papillary fronds with cellular atypia but no invasion through the basement membrane. This pattern is the key to the borderline diagnosis.
- Test for stromal invasion: Invasion of tumour cells into the ovarian stroma defines malignancy. Its presence moves the tumour from borderline to carcinoma.
- Grade the carcinoma: Low-grade tumours show low nuclear atypia with slow growth and KRAS or BRAF mutations. High-grade tumours show marked atypia and TP53 mutation.
- Note psammoma bodies: Their presence supports a serous origin but does not decide between benign, borderline and malignant lesions. Their absence does not exclude serous differentiation.
- Stage and examine the other side: Bilaterality, capsular breach and peritoneal spread determine the FIGO stage. Both ovaries and the peritoneum are assessed at surgery.
Where the exam tries to catch you
Serous questions test the criteria that separate benign, borderline and malignant tumours.
- Trap: Taking psammoma bodies as proof of malignancy. Correct: They occur in benign and borderline serous tumours too, so stromal invasion is the defining criterion.
- Trap: Assuming a bilateral serous tumour must be benign. Correct: Bilateral disease is more common in malignant serous tumours, so it raises suspicion of cancer.
- Trap: Assuming high-grade serous carcinoma arises only from the ovary. Correct: The fallopian tube is the proposed origin, so the tubes are examined carefully at surgery.
Frequently asked questions
Which histological feature defines a malignant serous ovarian tumour?
Stromal invasion, meaning tumour cells breaching the basement membrane into the ovarian stroma, defines a malignant serous ovarian tumour. Serous borderline tumours show atypia and papillary growth without this invasion. Grading then separates low-grade from high-grade serous carcinoma.
Are psammoma bodies specific for serous ovarian cancer?
Psammoma bodies are not specific for malignancy, because they occur in benign and borderline serous tumours too. They are also seen in meningioma, papillary thyroid carcinoma and mesothelioma. Their presence supports a serous origin but does not decide the grade or the behaviour of the tumour.
How does low-grade serous carcinoma differ from high-grade serous carcinoma?
Low-grade serous carcinoma has low nuclear atypia, slow growth and KRAS or BRAF mutations, and it responds less well to chemotherapy. High-grade serous carcinoma is the commonest ovarian cancer subtype, with marked atypia and TP53 mutation. It is generally more sensitive to platinum-based chemotherapy than the low-grade form.
Why does bilaterality matter in serous ovarian tumours?
Bilateral involvement is more common in malignant serous tumours than in benign cystadenomas, so it raises the suspicion of cancer. Bilateral disease does not by itself confirm malignancy, and histology is decisive. Both ovaries are examined and sampled as part of surgical staging.
Where does high-grade serous ovarian carcinoma arise?
High-grade serous ovarian carcinoma is thought to arise from the fallopian tube, through serous tubal intraepithelial carcinoma, rather than from the ovarian surface alone. This is why the fallopian tubes are examined carefully at surgery. The tubal origin also helps explain the strong association with BRCA mutations.