Yes, investigator b can use the specimens for cancer research without re-consent if the specimens are de-identified.
De-identification is the process of removing identifiers from human subject research specimens for the sake of privacy for research participants and to avoid leaking personal information.
Since the specimen has been de-identified it can not longer be connected to a specific individual. Thus, his/her identity is safe.
I attached the document I read that is the basis of my answer.
