Serous tumors are the most common of the ovarian epithelial tumors overall, and also make up the greatest fraction of malignant ovarian tumors. About 60% are benign, 15% are borderline, and 25% are malignant. Benign lesions are usually encountered in patients between 30 and 40 years of age, and malignant serous tumors are more commonly seen between 45 and 65 years of age.
There are two types of serous carcinomas, low-grade and high-grade. The former arise from benign or borderline lesions and progress slowly in a stepwise manner to become invasive carcinoma. These low-grade tumors are associated with mutations in genes encoding signaling proteins, such as KRAS, a member of the RAS gene family. The high-grade serous tumors develop rapidly. As already mentioned, many of these high-grade lesions arise in the fimbriated end of the fallopian tube via serous tubal intraepithelial carcinoma, rather than ovarian coelomic epithelium. TP53 mutations are virtually ubiquitous in high-grade serous cancers, being present in over 95% of cases. Other frequently mutated genes include the tumor suppressors NF1 and RB, as well as BRCA1 and BRCA2 in familial ovarian cancers.
Most serous tumors are large, spherical to ovoid, cystic structures up to 30 to 40 cm in diameter. About 25% of the benign tumors are bilateral. In the benign tumors, the serosal covering is smooth and glistening. By contrast, the surface of adenocarcinomas often has nodular irregularities representing areas in which the tumor has invaded the serosa. On cut section, small cystic tumors may have a single cavity, but larger ones frequently are divided by multiple septa into multiloculated masses. The cystic spaces usually are filled with a clear serous fluid. Protruding into the cystic cavities are papillary projections, which are more prominent in malignant tumors (
Fig. 19.16
On histologic examination, benign tumors contain a single layer of columnar epithelial cells that line the cyst or cysts. The cells often are ciliated. Psammoma bodies (concentrically laminated calcified concretions) are common in the tips of papillae. In high-grade carcinoma the cells are markedly atypical, the papillary formations are usually complex and multilayered, and by definition nests or sheets of malignant cells invade the ovarian stroma. Between clearly benign and obviously malignant forms
Fig.19.16Ovarianseroustumors.(A)Borderlineserouscystadenomaopenedtodisplayacystcavitylinedbydelicatepapillarytumorgrowths.(B)Cystadenocarcinoma.Thecystisopenedtoshowalarge,bulkytumormass.