Considering these issues, we hypothesized that the value of PgR as a biomarker for functional ER would be clearer if it were used as a dynamic biomarker, by FFNP-PET imaging of PgR levels in tumors before and then shortly after a brief, stimulating dose of estradiol: if tumor ER was functional, we expected to see an increase in FFNP-PET SUV, whereas the absence of an increase would suggest that ER was nonfunctional. The gene discussed is PGR; the disease is neoplasm.