I have just finished reading "My Dear Mr. Stalin. The Complete Correspondence of Franklin D. Roosevelt and Joseph V. Stalin, edited by Susan Butler, Yale University Press, 2005.
Aside from some very good source material on Poland, there is one revelation that can only be surmised with an advanced (post FDR's Deadly Secret) understanding of FDR's health.
p. 264 Stalin to Roosevelt, October 17, 1944
"Ambassador Gromyko has informed me about his recent conversations with Mr. Hopkins, in which Mr. Hopkins expressed an idea that you could arrive in the Black Sea at the end of November and meet with me on the Soviet Black Sea Coast. I would extremely welcome the realization of this intention. From the conversation with the Prime Minister (Churchill had just met with Stalin in Moscow), I was convinced that he also shares the idea. Thus the meeting of the three of us could take place at the end of November in order to consider the questions which have accumulated since Teheran. I would be glad to receive a message from you on this matter."
p. 265 Roosevelt to Stalin, October 23, 1944
I am delighted to learn from your message dated October 19 and from reports by Ambassador Harriman of the success attained by you and Mr. Churchill in approaching an agreement on a number of questions that are of high interest to all of us in our common desire to secure and maintain a satisfactory and durable peace. I am sure that the progress made during your conversations in Moscow will facilitate and expedite our work in the next meeting when the three of us should come to a full agreement on our fiture activities and mutual interests.
We all must investigate the practicability of various places where our meeting in November can be held (emphasis added) such as accessibility, living accomodations, security, etc., and I would appreciate suggestions from you. I have been thinking about the practicabilty of Malta, Athens, or Cyprus if my getting into the Black Sea on a ship should be inpracticable or too difficult, I prefer traveling and living on a ship.
p. 267 Roosevelt to Stalin November 18, 1944
All three of us are of one mind- that we should meet very soon, but problems chiefly geographical do not make this easy at this moment. I can, under difficulties arrange to to go somewhere now in order to get back here by Christmas, but, quite frankly, it will be far more convenient of I could postpone it until after the Inauguration which is on January twentieth.
FDR then goes on to make excuses for the dealy based on "constitutional obligations".
Just as the April 1944 Bermuda summit had to be cancelled due to FDR's health (this is not speculative, see details in the book) so, most probably, did the Yalta conference have to be delayed.
The more likely reality:
Fdr's health worsened necessitating a postponement and trip to Warm Springs to recuperate (his first visit there since April 1943). I initially thought that the operation describd below was the reason but a re-reading of the Suckley diary makes that possibility very weak- There was not enough time to allow for recovery. When the operation took place is still unknown- so many layers of smokescreen!
There is ever increasing evidence of a top secret operation (still!) at Lahey, largely based on information gathered by Dr. Harry Goldsmith and personal conversations with Dr. Ruben Oropeza, a close confidante and protege of Dr. George T. Pack. Most probably, the primary surgeon was Pack (the greatest melanoma surgeon of the twentieth century) assisted by Frank Lahey (a world-reknowned abdominal surgeon) Richard Cattell (Lahey's number 2 and head of the clinic after Lahey's death in 1953) and Isador Ravdin (renowned surgeon from the University of Pennsylvania who later operated on Dwight Eisenhower's ileitis. Ravdin had been stationed in Burma (where he treated Mountbatten), but did return to the US once in 1944).
By all reports, the surgery was "open and close" after the discovery by the surgeons of widespread abdominal and liver metastases.
No, we can't prove it, though the records are probably sequestered in the Boston area. Let's just call it "educated speculation".