Palbociclib Combined With Afatinib for Advanced Squamous Carcinoma of Esophagus or Gastroesophageal Junction

Inclusion Criteria: * Pathologically confirmed metastatic or inoperable locally advanced squamous carcinoma of the esophagus or gastroesophageal junction that is not amenable to radical radiotherapy. * Prior progression to at least first-line chemotherapy which must include immune checkpoint inhibitors (except in patients with contraindications to immune checkpoint inhibitors). Adjuvant/neoadjuvant therapy is allowed and is considered first-line therapy for advanced disease if recurrence occurs during or within 6 months of completion of adjuvant/neoadjuvant therapy. * At least one measurable tumor lesion according to RECIST V1.1 criteria. A lesion previously treated with radiotherapy is not acceptable as a target lesion unless the lesion is significantly progressive. * Sign the informed consent form * 18\~75 years * Performance status: ECOG 0-1 * Good organ function: Blood routine: hemoglobin ≥90g/L, neutrophil ≥1.5×10\^9/L, platelet ≥100×10\^9/L; Renal function: creatinine≤1.5×upper limit of normal (UNL) or creatinine clearance ≥50ml/min; Liver function: total bilirubin (TBIL)≤1.5×upper limit of normal (UNL); ALT≤2.5×UNL, AST≤2.5×UNL; Ejection fraction at least 50% (or lower limit of normal) by echocardiogram Exclusion Criteria: * Other pathological category, such as adenocarcinoma, adenosquamous carcinoma * Have received CDK4/6 inhibitors or anti-EGFR targeted drugs in the past * Known to have allergic reactions to any ingredients or excipients of experimental drugs * Unable to swallow or under other circumstance which would drug absorption * Other active malignant tumors, excluding those who have been disease free for more than 5 years or in situ cancer considered to have been cured by adequate treatment * Diabetes was not controlled, defined as HbA1c \> 7.5% after anti-diabetic drugs or hypertension was not controlled, defined as systolic / diastolic blood pressure \> 140 / 90 mmHg after antihypertensive drug * Myocardial infarction, severe/unstable angina, New York Heart Association (NYHA) class III or IV congestive heart failure in the past 12 months * Known to be infected with human immunodeficiency virus (HIV), have acquired immunodeficiency syndrome (AIDS) related diseases, have active hepatitis B or hepatitis C * Pregnant or nursing * May increase the risk associated with participation in the study or administration of the study drug or mental illness that may interfere with the interpretation of research results * There are other serious diseases that the researchers believe patients cannot be included in the study