Using Scatchard-type plot (Fig. 5G), we calculated the dissociation constant (KD) of the binding between serglycin isolated from breast cancer cells and C1q to be 0.2×10−7 M. The affinity of the interaction between breast cancer-derived serglycin and C1q was slightly higher than the affinity between multiple myeloma cell-derived serglycin and C1q (KD = 0.4×10−7 M). Here, SRGN is linked to AL amyloidosis.