Study of Dalpiciclib Isethionate Plus Pyrotinib Maleate in the Treatment of Advanced Esophageal Squamous Cell Carcinoma

Dalpiciclib Isethionate tablets, 125mg, oral administration on days 1 to 21, followed by a 7-day drug holiday, every 4 weeks; Pyrotinib Maleate tablets, 320mg, oral administration once daily on days 1 to 28, every 4 weeks; Treatment will continue until disease progression, intolerable toxicity, initiation of new antitumor therapy, withdrawal of informed consent, or the investigator determines that the subject should discontinue study treatment.