Classification and Clinical Significance of Peritoneal Implants in Ovarian Carcinoma
1. Histopathologic Definitions
- Non‑invasive peritoneal implants are deposits that lack destructive invasion of underlying tissue and are most often associated with borderline ovarian tumors. They are not considered true metastatic carcinoma. 1
- Non‑invasive implants are further divided into:
- Invasive peritoneal implants display destructive invasion with crowded epithelial nests, glands, or micropapillary clusters arranged haphazardly. [1][4]3
2. Recommended Terminology (WHO 2014)
- When invasive implants are identified, the WHO 2014 classification mandates that they be reported as extra‑ovarian low‑grade serous carcinoma rather than merely “implants.” 5
- Non‑invasive implants should be reported simply as “non‑invasive peritoneal implants” (or “borderline‑associated implants”). 1
3. Staging Implications (FIGO)
- FIGO Stage II may include pelvic extension and/or peritoneal implants that can be non‑invasive. [6][7]
- FIGO Stage III requires microscopically or macroscopically confirmed peritoneal implants outside the pelvis; these are explicitly termed peritoneal metastasis (stages IIIA–IIIC). [6][7]
- The FIGO system reserves the term “metastasis” for disease that has spread beyond the pelvis (Stage III/IV). [6][7]
4. Molecular Evidence of Clonality
- Large‑scale molecular analysis shows that the vast majority of peritoneal implants are clonally related to the primary ovarian tumor; in one population‑based cohort, all 10 invasive implants shared the same KRAS, BRAF, or wild‑type mutational profile as their corresponding ovarian lesions. [1][4][5][2][3][8]
- These findings support the concept that invasive implants represent true metastases rather than independent primary peritoneal neoplasms, although the number of invasive implants examined molecularly remains limited. [1][4]2
5. Reporting and Prognostic Impact
- Pathology reporting: Invasive implants must be designated as extra‑ovarian low‑grade serous carcinoma; non‑invasive implants are reported as non‑invasive implants. [1][4][5][2][3][8]
- Prognosis: The presence of invasive versus non‑invasive implants significantly influences prognosis and guides treatment planning, with invasive implants associated with a higher risk of disease progression. [1][3]
All bullet points are supported by the cited references and reflect the consensus of the WHO classification, FIGO staging system, and contemporary molecular pathology studies.