Threats, competition, the patent. I don't know but it is as credible a speculation as any. They are a smaller company. Maybe they felt secrecy was the best policy and a surprise attack for this little company. Again I don't know but it sure fits the timeline.
If this is the case, they couldn't because it could compromise the trial integrity and the double blind nature: Because the patients / physicians can get influenced by the disclosure of the more potent DCVAX being administered and the results collected will be inadmissible.
The theory would be a good and straightforward explanation though for many of the things: delays, secrecy over the halt etc.