RESUMO
BACKGROUND: Low-grade serous carcinoma (LGSC) of the ovary, which is extremely rare tumor, has better prognosis than high-grade serous carcinoma (HGSC). Genetic backgrounds of those are different, so that LGSC usually shows KRAS or BRAF mutation, whereas HGSC does not show such mutations. Since treatment strategies of those are different, differential pathological diagnosis between LGSC and HGSC is very important. CASE: We report a case of LGSC that was diagnosed by both cytological findings and genetic analysis using small amount cells from cytological specimen. The 30-year-old Japanese woman with bilateral ovarian tumors underwent salpingo-oopherectomy. The peritoneal washing cytologic specimen and touched cytologic specimen from the tumor included non-complex clusters with psammoma bodies composed of tumor cells with mild to moderate atypia and without bizarre nuclei. The ovarian tumor was histologically diagnosed as LGSC. The genetic analysis that was done using exfoliated cells from peritoneal washings specimen by idensy™, detected KRAS mutation at codon 12/13. CONCLUSION: The genetic investigation using cytological specimen as well as characteristic cytological findings were useful to make differential diagnosis between LGSC and HGSC.