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There are some rare types of ovarian cancer that cannot easily be classified using the classification of epithelial cells, sex cord-stromal cellssteroid cells or germ cells

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Small cell ovarian carcinoma

This is an aggressive type of ovarian cancer with a tendency to grow quickly. It most commonly develops in young women (below the age of 30) and is often associated with a high calcium level in the blood (hypercalcaemia).

There are three main variants of small cell ovarian carcinoma:

  • Small cell ovarian carcinoma pulmonary type (SCOCPT) is extremely rare, accounting for less than 0.5 per cent of ovarian cancers diagnosed. It is an epithelial tumour and is treated in the same way as a small cell carcinoma that originates in the lung with a combination of surgery, chemotherapy and radiotherapy.
  • Small cell carcinoma of the hypercalcemic type (SCCOHT). This is now recognised as a type of tumour called a rhabdoid tumour. This means it does not originate from epithelial cells and is associated with somatic or germline mutations in the SMARTCA4 gene. The best treatment for these tumours has yet to be defined but usually involves a combination of surgery and chemotherapy. There may be a role for radiotherapy in selected cases.
  • Large cell variant of small cell carcinoma or non-small cell carcinoma (NSCSCC). They are usually treated as aggressive epithelial ovarian carcinomas, not as small cell carcinomas. 

Unfortunately with so few cases of small cell ovarian cancer there has been relatively little research into new drugs specifically targeting this type. There has been a recent review of cases of small cell ovarian carcinomas which concluded that surgery is appropriate treatment, especially in very early stages of disease, but chemotherapy should also be considered.

Neuro-endocrine carcinomas

These are extremely rare tumour types that are primarily treated with surgery but may involve chemotherapy and other drugs. There are variants:

  • Non-small cell neuro-endocrine carcinoma (large cell variant) (NSCNEC)

  • Classical primary carcinoid (well differentiated neuroendocrine cancer)

  • Classical carcinoid metastatic from primary gastrointestinal site

  • Atypical carcinoids or high grade neuroendocrine carcinomas can also rarely occur.

    Treatment with somatostatin analogues (drugs which slow down the production of hormones) could help to control symptoms and stabilise these slow-growing tumours.

    Two women talking

    Squamous cell carcinoma rising within dermoid cyst

    Dermoid cysts (or mature teratomas) are the commonest ovarian tumours and are nearly always benign (non-cancerous). However, in a rare number of cases (one to two per cent) these can be malignant (cancerous), typically in postmenopausal women.

    Squamous cell carcinoma (SCC) is the most common type of cancer that arises from a dermoid cyst. They are often diagnosed late because of symptoms of pressure symptoms or torsion (twisting of the ovary) and the resulting abdominal/tummy pain, and usually occur in older women. If diagnosed at an early stage, these can usually be treated by surgery alone. For more advanced stages, surgery may need to be combined with chemotherapy; however, because these tumours are extremely rare, the best type of chemotherapy has yet to be defined.

    Struma ovarii malignum

    Struma ovarii is a variant of mature teratoma which contains thyroid tissue. They account for only three per cent of ovarian teratomas and generally have a low malignant (cancerous) potential so can usually be successfully treated with surgery alone. In younger women, conservative fertility-sparing surgery can be considered, to preserve the possibility of becoming pregnant later on, with possible further surgery after a woman has completed her family. Read our Younger women section for more information on fertility-sparing surgery.

    Psammocarcinoma

    Serous psammocarcinoma is a rare variant of serous carcinoma arising either from cells in the ovary or peritoneum. It is usually treated by surgery alone, although in some cases chemotherapy will also be used. As this type of ovarian cancer is so rare, the best type of treatment has not yet been identified. 

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    Last reviewed: June 2018
    Next review: May 2021