Patients with cancer often experience intertwined symptom burden and functional decline that contribute to falls, unsafe transfers, uncontrolled symptoms, caregiver strain, and crisis-driven care. Physical medicine and rehabilitation (PM&R), also known as physiatry, and specialty PC both address suffering and quality of life through complementary clinical approaches; however, collaborative care with and between these two specialties is inconsistent in routine oncology practice. This paper presents a clinical implementation framework informed by targeted literature synthesis for bidirectional referral and co-management between PM&R and PC in oncology. The framework was informed by the PC referral criteria literature, cancer rehabilitation triage literature, trigger-based serious illness identification models, and implementation science. Four clinic-usable tools are proposed, including a scope and overlap map, a clinical-needs gradient, a referral trigger table linking common clinical signals to the reason for referral and expected clinical actions, and a primary-service triage workflow. This framework is intended to clarify which service is best positioned to be the primary supportive service according to the patient’s current needs, when rehabilitation therapy alone may be sufficient, and when co-management should be the default. This concept-to-practice model is designed to facilitate early, needs-based referrals and coordinated supportive care in oncology settings.