Ovarian Tumors - Complete Classification, Etiology, Pathogenesis, Morphology, Clinical Course, Spread & Complications

1. Overview & Epidemiology

2. Classification of Ovarian Tumors

3. Epithelial Ovarian Tumors (Most Important)

Histologic Subtypes (WHO Classification)

Key Concept: Type 1 vs. Type 2 Serous Tumors

4. Etiology & Risk Factors

Genetic / Hereditary Factors

• BRCA1 (chromosome 17q12-21): Lifetime ovarian cancer risk 39-63%; BRCA2 (13q12-13): 16.5-27%
• BRCA1/2 are components of the homologous DNA double-strand break repair machinery
• Women with BRCA1 mutations typically develop ovarian cancer in their 40s-50s; BRCA2 carriers in their 50s-60s
• Lynch syndrome (MLH1, MSH2, MSH6, PMS2 mutations) - associated with endometrioid ovarian tumors
• PALB2 and other homologous repair genes also confer risk

Hormonal / Reproductive Factors ("Incessant Ovulation" Hypothesis)

• Nulliparity and infertility - increased risk
• Early menarche and late menopause (longer ovulatory career) - increased risk
• Hormone replacement therapy (controversial)
• Protective: Oral contraceptive use (50% risk reduction with 5+ years use), multiparity (0.3-0.4 risk reduction per child), tubal ligation, breast-feeding, aspirin use

Environmental Factors

• Obesity, high-fat diet
• Talc exposure (controversial, peritoneal route)
• Infertility treatments

5. Pathogenesis

Modern Understanding: Fallopian Tube Origin

• Most high-grade serous carcinomas originate from the fimbriated end of the fallopian tube
• Serous tubal intraepithelial carcinoma (STIC) lesions are identifiable in risk-reducing salpingo-oophorectomy specimens from BRCA carriers
• Clear cell and endometrioid types arise from endometriosis

Molecular Pathogenesis

1. Germline or somatic loss of BRCA1/2 function in fallopian tube epithelium
2. TP53 mutation (seen in ~95% of cases) - the earliest detectable change
3. Intraepithelial carcinoma (STIC) forms in the tubal fimbriae
4. Tumor cells shed from the tube, spread to the ovarian surface and peritoneal cavity
5. MUC16 (CA-125) expression on cancer cells facilitates binding to mesothelin on peritoneal cells
6. Widespread genomic instability: amplifications, deletions (NF1, RB1, CDK12)

• Stepwise progression: benign → borderline → invasive (the "adenoma-carcinoma sequence")
• Driven by activating mutations in KRAS, BRAF (MAP kinase pathway), PTEN, PIK3CA

6. Pathology & Morphology

Serous Tumors

• Borderline: Complex papillary fronds with hierarchical branching, lined by pseudostratified columnar cells; NO stromal invasion
• Malignant (high-grade): Marked nuclear atypia, brisk mitoses, stromal invasion, gland formation and solid areas
• Psammoma bodies (concentric calcification rings) - characteristic but not exclusive to serous tumors

Serous borderline tumor of the ovary: complex papillary fronds lined with pseudostratified columnar cells (Berek & Novak's Gynecology)

Endometrioid Tumors

• Represent 6-8% of epithelial tumors
• Associated with endometriosis (Sampson's theory, 1925)
• Histology: markedly complex glandular pattern resembling proliferative endometrium; confluent back-to-back glands
• 15-20% are synchronous with endometrial carcinoma - if both are well-differentiated with superficial endometrial invasion, these are considered independent primaries (75-80% 5-year survival vs. 30-40% for metastases)

Endometrioid carcinoma of the ovary: round to tubular glands lined by stratified columnar cells with a confluent growth pattern (Berek & Novak's Gynecology)

Mucinous Tumors

• Lined by mucin-secreting epithelium resembling GI or endocervical epithelium
• Often very large, multiloculated cysts
• Pseudomyxoma peritonei - accumulation of gelatinous mucinous material in the abdominal cavity; most commonly from appendiceal mucinous neoplasms, rarely from primary ovarian mucinous tumors

Clear Cell Carcinoma

• Patterns: tubulocystic, papillary, reticular, solid
• Cells have abundant clear/vacuolated cytoplasm; "hobnail cells" project nuclei apically
• Almost invariably high-grade nuclei
• Strongly associated with endometriosis; histologically identical to clear cell carcinoma of DES-exposed uteri

Borderline Tumors (Low Malignant Potential)

• Show increased cell proliferation but lack stromal invasion (this is the defining criterion separating borderline from invasive)
• Occur predominantly in premenopausal women (ages 30-50)
• Very good prognosis
• Extraovarian implants may occur; invasive implants (analogous to low-grade serous carcinoma) have higher risk of progression and can cause intestinal obstruction from fibrosis

7. Germ Cell Tumors (15-20% of all ovarian tumors)

8. Sex Cord-Stromal Tumors (~8%)

9. Clinical Course & Presentation

Symptoms (Notoriously Vague and Late)

• Abdominal distension and/or pain
• Change in appetite, early satiety
• Weight gain and increased girth (ascites)
• Urinary frequency/obstruction
• Over half present to non-gynecological specialties first with GI disturbance, shortness of breath, or change in bowel habit from metastatic disease

Physical Examination

• Pelvic mass (often detected late)
• Ascites
• Pelvic mass + ascites = ovarian cancer until proven otherwise (but consider Meigs' syndrome - benign fibroma with ascites and pleural effusion)

10. Spread & Metastasis

1. Direct Peritoneal Seeding (Most Common Route)

• Malignant cells shed from the tumor surface into the peritoneal cavity
• Implant throughout the peritoneum: undersurface of the right hemidiaphragm, omentum, paracolic gutters, bowel serosa, bladder reflection, cul-de-sac
• Omental caking - characteristic matted omental metastasis
• Facilitated by MUC16 (CA-125) binding to mesothelin on peritoneal cells

2. Lymphatic Spread

• To pelvic and para-aortic lymph nodes
• Less common initially but present in advanced disease

3. Hematogenous Spread

• Late; to liver parenchyma, lungs (Stage IV)
• Pleural effusion also common in advanced disease

FIGO Staging

~70% of patients present at Stage III or IV, explaining the poor overall survival.

11. Complications

• Intestinal obstruction - from peritoneal/omental metastases and adhesions (especially borderline tumors with invasive implants); a major cause of death
• Malignant ascites - massive fluid accumulation, abdominal discomfort, dyspnea
• Pleural effusion - from diaphragmatic involvement or pleural seeding
• Hydronephrosis / ureteral obstruction - from retroperitoneal disease
• Ovarian torsion - complication of large benign/malignant ovarian masses
• Tumor rupture - peritoneal contamination, upstages disease
• Hormonal effects - endometrial hyperplasia/carcinoma (from estrogen-secreting granulosa cell tumors); virilization (Sertoli-Leydig tumors); precocious puberty (granulosa cell tumors in children)
• Paraneoplastic syndromes - e.g., inflammatory limbic encephalitis (associated with mature teratomas)
• Pseudomyxoma peritonei - gelatinous ascites from mucinous tumors

12. Investigations

• Ultrasound (transvaginal) - first-line; characterizes morphology (IOTA criteria)
• CA-125 - elevated in 50% of Stage I and >90% of advanced serous disease; non-specific (also elevated in endometriosis, PID, other cancers); normal cut-off 35 U/mL
• CT/MRI - staging; assesses peritoneal disease, lymphadenopathy, distant spread
• Tumor markers by age/type:
  • AFP + β-hCG + LDH: women <40 to exclude germ cell tumors
  • Inhibin: granulosa cell tumor marker
  • CA-19-9, CEA: for mucinous tumors
• Risk of Malignancy Index (RMI) = menopausal status × ultrasound score × CA-125 level

13. Management Overview

Surgery

• Cytoreductive (debulking) surgery via midline laparotomy is the cornerstone
• Includes: peritoneal washings, infracolic omentectomy, pelvic/para-aortic lymphadenectomy, bilateral salpingo-oophorectomy + total abdominal hysterectomy, biopsy of suspicious lesions
• Appendicectomy for mucinous tumors
• Goal: no residual disease (optimal cytoreduction)
• Fertility-sparing (unilateral oophorectomy) allowed for Stage IA/IB low-grade or borderline tumors

Chemotherapy

• Platinum-based (carboplatin/paclitaxel) combination: standard first-line for advanced disease
• BRCA1/2-mutated tumors respond to PARP inhibitors (olaparib, niraparib, rucaparib)

Prevention

• Oral contraceptives: 50% risk reduction with >5 years of use; 70% reduction in women with 2+ children who used OCPs >5 years
• Prophylactic bilateral salpingo-oophorectomy for BRCA1/2 carriers (ideally before age 40 after childbearing complete)
• Note: prophylactic salpingo-oophorectomy does not completely eliminate risk - peritoneal carcinoma can still occur in 2-3% of cases

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