If indeed Chavez had a type of sarcoma of or involving the psoas muscle here is a brief medical abstract on the topic...
http://publications.icr.ac.uk/1751/
Surgery was done in 14 patients (negative microscopic margins-7, positive microscopic margins-3, and positive gross margins-3 and the margin of excision was not known in I patient). Five of 14 surgically treated patients had local recurrence and 6 of 19 patients developed metastases. Ten patients died of their disease at a median follow-up of 12 months. The estimated 2 and 5 year survival rates were 44 and 23%, respectively. Conclusions: Tumors in this location have a poor prognosis due to the lack of early diagnosis, large size at presentation, multiple attachments of the psoas muscle, and being relatively surgically inaccessible. (My emphasis.)
IOW, Hugo was in deep, brown smelly stuff from the moment he was diagnosed, needed the best available care, and chose to go with Obama/CastroCare instead, with the inevitable outcome.