Does soluble fms-like tyrosine kinase-1 regulate placental invasion? Insight from the invasive placenta

Soluble fms-like tyrosine kinase (sFLT-1) is a potent antiangiogenic growth factor that has been found to be markedly elevated in preeclampsia. In healthy pregnancy, serum sFLT-1 concentrations are 50-fold higher than in the nonpregnant state. The functional significance of this physiologic elevation in serum sFLT-1 in normal pregnancy is unknown. We hypothesized that sFLT-1 regulates placental cytotrophoblast invasion and that lower levels of sFLT-1 would be observed locally in invasive placentas (accreta/increta/percreta).

We performed a retrospective case-control study comparing placental sFLT-1 expression in hysterectomy specimens from 3 groups: group 1, focally invasive placenta; group 2, normal invasion from the same specimen; and group 3, normal invasion associated with placenta previa. Immunohistochemistry for sFLT-1 was performed, and staining intensity was graded on a scale from 1+ (weak) to 5+ (strong).

We identified 10 hysterectomy specimens from women with invasive placentation and 3 with placenta previa. The median sFLT-1 staining score for group 1 was 1.75 compared to 4.0 for group 2 (P = .01). A significant difference was also found between group 1 and group 3 (P = .01). When comparing depth of invasion, there was a trend toward lower staining score as depth of invasion increased (P = .11). Interobserver agreement for immunohistochemistry scoring was 87%.

Lower levels of sFLT-1 protein expression were associated with invasive placentation suggesting a critical functional role for sFLT-1 in regulation of placental invasion.