A policy analysis paper from the Cato Institute
talks about the 2-4-D studies and particularly the dog study. The full
text can be found at http://www.cato.org/pubs/pas/pa366.pdf,
look at pages 8 and 9. They are basically saying that the data does not
support the conclusion. Since 1991 (the date of the original study)
no one has been able to duplicate the original findings of a correlation between
home use of 2-4-D and cancer in pets. This does not mean it is perfectly
safe but it does appear that the concerns are over stated.