FAP and neoplasm: As shown in Figures 4A, 4B, and 4C, FL-L3-99mTc was observed to accumulate in MDA-MB231 solid tumors (2.23% ID/g) and a co-injection of excess of FL was seen to block this tumor uptake (0.13 ± 0.06 %ID/g), suggesting that tumor retention was FAP-mediated.