Malignant? By pituitary cancer I am assuming you mean malignant cancer and not tumor (that is benign). Pituitary dysfunction can occur because the normal tissue is crowded out by the cancer. There could be problems with steroid production during times of stress, reproductive problems like low testosterone or irregular menstrual cycles, & thyroid dysfunction. Some pituitary cancers can cause excess hormones.
Affect many hormones. Pituitary tumors can affect a broad number of hormonal axis in our body including thyroid function, menstrual cycles in women, the ability of pregnant women to lactate, testosterone production in men, the ability to produce cortisol, influence body size in general, while also affecting our kidney's ability to retain water.