In case of prostate cancer the cause of spontaneous fracture may be:
Metastatic tumour in the bone leading to weakness at that site and subsequent fracture even with minimal trauma, or
due to osteoporosis and bone weakness.
Furthermore, Androgen ablation therapy (which includes Bicalutamide i.e Tabi in your father's case) further increases the chances of osteopenia and bone weakness. According to one estimate, 4 years of Androgen deprivation therapy will place the average man in the osteopenia range thus increasing the risk of fracture.
Treatment of osteoporosis begins with early recognition and also taking preventive measures. Smoking cessation, weight bearing exercise, and vitamin D and calcium supplements can help improve bone mineral density. Additionally, in patient receiving androgen deprivation therapy, Bisphophonate therapy (Zoledronic acid) may also be indicated.Anaemia (i.e. low hemoglobin) may be because of lack of testosterone stimulation of red blood cell precursors in the bone marrow in patients receiving Androgen deprivation therapy. In advanced cases of prostate cancer, tumour growth in bone marrow spaces further compromises the red blood cell production.There are few case reports in the literature suggesting drug induced eosinophilia from the drug bicalutamide (Tabi).