What does TK mean?

In the ARC of The Lost City of Z, there are several places where "TK" or "tk" appear in the text, a la "She only lived for a few more years, dying of TK in 19-tk." It's the first time I've noticed something like that.

Obviously it's being used as a placeholder for information to be added in later, but I was wondering if anyone knew if this is common, what TK stands for, or anything about its use. (Googling "TK" is not particularly enlightening.)

It's a proofing/copyediting mark that is short for "to come"—don't know why it's a K and not a C...but... But yes, it's common in editing.

What's TK mean in this case?

http://www.librarything.com/author/3505002205

Someone's going to come back and give the author later on?

I thought it might have been a German abbreviation, but it seems that it is not, and there is a good explanation here:

http://en.wikipedia.org/wiki/To_come_(publishing)