Celldex Therapeutics Inc., of Needham, said its Phase 2b study of the experimental treatment CDX-011 ­— for patients with a certain type of advanced breast cancer — showed an overall survival benefit. Brean Capital called the results impressive, telling clients the drug “targets a clear and large unmet need.” Celldex’s chief medical officer said the company will have talks with the FDA this month on “a pivotal study” designed to pave the way for marketing approval.