Additional Study Information: The purpose of this study is to study SGN-B6A alone, with pembrolizumab, or with pembrolizumab and one of the chemotherapy drugs (cisplatin or carboplatin). The sponsor wants to find out what its side effects are and if it works for specific types of cancer. It is not yet known if SGN-B6A alone or with other drugs is better or worse than other treatments. This clinical trial uses an experimental drug called SGN-B6A. This means the Food and Drug Administration (FDA) hasn't approved it for sale in the United States. This clinical trial also uses pembrolizumab. Pembrolizumab is approved by the FDA to treat several types of cancer. This clinical trial also uses the chemotherapy drugs cisplatin and carboplatin. Cisplatin and carboplatin are chemotherapy drugs approved by the FDA to treat multiple kinds of cancer. Cisplatin and carboplatin both use platinum to fight tumor cells. Thousands of patients with cancer have already been given cisplatin and carboplatin. Cancers include lung cancer, and head/neck and oral cancer.