While the ≥1% threshold used for positive tumor status for PD-L1 or PD-L2 is lenient, the identification of PD-L1-negative ER+ tumors that expressed significant levels of PD-L2-positive cancer cells supported the possibility that combined analysis of PD-L1 and PD-L2 will better predict the response to PD-1i than PD-L1 alone, and may be of value in determining treatment options for aggressive ER+ tumors. Here, PDCD1LG2 is linked to cancer.