Testing the Addition of Radiotherapy to the Usual Treatment (Chemotherapy) for Patients With Esophageal and Gastric Cancer That Has Spread to a Limited Number of Other Places in the Body

Inclusion Criteria: * REGISTRATION TO STEP 1 * Patient must have histologically confirmed HER2 negative metastatic esophageal or gastric adenocarcinoma (American Joint Committee on Cancer \[AJCC\] 8th edition) * Patient must have oligometastatic disease at the time of registration, which is defined as the following: * At most 3 radiologically visible metastatic lesions (not sites), in addition to the primary site. Computed tomography (CT) or magnetic resonance imaging (MRI) scans will be performed for staging purposes. Patients with oligometastatic sites that are only detected with positron emission tomography (PET)/CT will be eligible for participation, as long as radiation planning and administration is feasible after discussion with treating radiation oncologist. Malignant lymph node should be at least 1 cm in size or biopsy proven involved by disease * Anatomically defined lymphadenopathy will be considered as 1 site of metastatic disease. For example, 2 enlarged paraaortic lymph nodes will be considered as one site, and 2 additional sites will be allowed to meet protocol definition of oligometastatic disease. However, if supraclavicular or cervical nodes are involved for distal esophageal tumors or gastric tumors, these are counted separately from intrathoracic nodes. For upper thoracic/cervical esophageal tumors, the involvement of celiac nodes are counted separately from intrathoracic nodes. Intrathoracic nodes, defined as hilar and mediastinal nodes, will be col…