Staging and treatment of ovarian carcinoma

Dynamic alterations of the extracellular environment of ovarian surface epithelial cells in premalignant transformation, tumorigenicity, and metastasis

BACKGROUND

Ovarian surface epithelial cells are positionally organized as a single cell layer by a sheet of basement membrane. It is believed that the contact of the ovarian surface epithelial cells with the basement membrane regulates cell growth and ensures the organization of the epithelium. Disabled-2 (Dab2), a signal transduction protein and a candidate tumor suppressor of ovarian carcinoma, functions in positional organization of ovarian surface epithelial cells. In ovarian carcinomas, genetic and epigenetic changes enable the tumor cells to escape positional control and proliferate in a disorganized fashion. Alterations in the extracellular environment may also be critical for tumor initiation and progression.

METHODS

We analyzed and compared the presence of collagen IV and laminin, the scaffold proteins of the basement membrane, and Dab2 in 50 ovarian tumors that are restricted to the ovaries and in 50 metastases of ovarian tumors by immunohistochemistry. Expression of collagen IV, laminin, and Dab2 was also analyzed by Northern blotting in a panel of human ovarian surface epithelial and cancer cell lines.

RESULTS

The basement membrane is often absent in morphologically benign ovarian surface and cyst epithelium and low-grade tumors and collagen IV and laminin are absent in the extracellular matrix of most of the primary tumors tested. Of the 50 ovarian tumors confined to the ovaries, 6% (3 of 50) were collagen IV positive and 24% (12 of 50) were laminin positive tumors. Of the 50 metastatic tumors, 16% (8 of 50) are collagen IV positive and 86% (43 of 50) are laminin positive. In addition, even in the metastatic ovarian tumors that are largely collagen IV negative, there are pockets of local areas in which the tumor cells are surrounded by collagen IV-positive staining. Dab2 is absent in the majority of ovarian tumors found in both ovaries and metastatic sites. In both nontumorigenic human ovarian surface epithelial and cancer cell lines, collagen IV, laminin, and Dab2 are expressed aberrantly.

CONCLUSIONS

Loss of the basement membrane may be an early event in the preneoplastic transformation of ovarian surface epithelium and in the early stages of tumorigenesis before tumor invasion and metastasis. The majority of primary ovarian tumors examined lack collagen IV and laminin in their extracellular matrix. However, expression of laminin is restored in the majority of metastatic tumors. Reexpression of collagen IV may also contribute to tumor metastasis. The ability of tumor cells to dynamically alter the expression of collagen IV and laminin may facilitate the shedding of cancer cells into the peritoneal spaces and subsequent attachment to the metastatic sites. We propose that loss of collagen IV and laminin may be an initial event in ovarian tumorigenicity and that restoration of collagen IV and laminin expression in the later stages of tumor development may promote metastasis of ovarian tumors.

Imaging of ovarian cancer

Cross sectional imaging continues to play an increasingly important role in ovarian cancer diagnosis, staging, and treatment follow-up. Screening for ovarian cancer remains a controversial subject. The combined use of clinical examination, CA-125, and endovaginal ultrasound (US) are being advocated for high risk patients but consensus recommendation for screening awaits further studies. In characterization of an ovarian neoplasm US is indisputedly the primary imaging approach. Only when US is inconclusive are further studies warranted. Magnetic resonance imaging (MRI) is generally preferred to computer tomography (CT). A prospective MRI-CT clinical trial has not been performed as yet. Preoperative staging by imaging is slowly gaining its acceptance. This is mostly due to the awareness of the difficulties and inaccuracy in surgical staging when unsuspected extensive disease is present. Furthermore, in known resectable ovarian cancer, primary chemotherapeutic cytoreduction may be a better treatment option. Accuracy of CT and MRI in staging ovarian cancer is similar, CT, however, is faster, more widely available, and less expensive; these are important attributes that are decisive in this time of health reimbursement constraints.

External beam radiotherapy in the management of ovarian carcinoma

Between 1970 and 1983, 345 patients with ovarian cancer clinical stage I, II, and III were irradiated postoperatively. Five-year NED survival was achieved in 41.7% of patients. The most important prognostic factors were histological grade and clinical stage of cancer. Postoperative external beam radiotherapy appeared to be highly efficient for the patients with microscopic residual disease, giving 70% 5-year survival, and moderately efficient for patients with small, i.e. < or = 3 cm in diameter residual disease, giving 40% 5-year survival. The optimal technique of irradiation appeared to be the irradiation given to the entire abdominal cavity with additional irradiation coned down to the pelvis. External beam radiotherapy was ineffective in patients with gross residual disease, i.e. > 3 cm in diameter, and useless as palliative treatment given to patients with inoperable cancer of the ovary.