The actual diagnosis of your brother is not mentioned here, lung cancer
may be of two major types, small cell lung cancer and non small cell lung cancer. Anyway, chemotherapy regimens
are different in these two disease. Steroid can rapidly increase the body weight but there is no uniform consensus regarding its use for this indication, that depends on treating physician. Steroid use can have side effects like excessive sweating
, consult your oncologist
for dose modification if he/she thinks so.