Chemical modification of natural human tumor necrosis factor-α with polyethylene glycol increases its anti-tumor potency - Tsutsumi, Y; Kihira, T; Yamamoto, S; Kubo, K; Nakagawa, S; Miyake, M; Horisawa, Y; Kanamori, T; Ikegami, H; Mayumi, T (Jpn J Cancer Res, 1994)