Serous ovarian tumors of low malignant potential (SLMP) - also called borde
rline tumors of the ovary - represent a heterogeneous group of ovarian epit
helial neoplasms. In general, this tumor type has a favorable prognosis. Ne
vertheless, 10-20% of SLMP exhibit a progressively worsening clinical cours
e, with widespread peritoneal implants and death of the patient within 5 ye
ars. The criteria for recognizing the SLMP with an unfavorable prognosis an
d for distinguishing SLMP from highly differentiated ovarian carcinomas are
summarized in this report. The importance of supporting methods, e.g., DNA
cytophotometry, is demonstrated, revealing that in most cases aneuploidy c
an be regarded as an indicator for aggressiveness of the tumor and for poor
clinical outcome. The importance of the new concept of micropapillary sero
us carcinomas (MPSC), the relationship of this variant of SLMP to invasive
serous carcinomas, and the prognostic importance of invasive vs noninvasive
peritoneal implants are discussed. (The concepts of molecular pathology of
SLMP will be discussed in part 2 of this serial paper.)