Focuses on three complex non-epithelial entities that demand specialized algorithms. For GIST, diagnosis is based on CD117 (KIT) and DOG1, and management hinges on molecular genetics (Exon 11 is favorable; Exon 9 requires higher imatinib dosing). Rectal GIST presents a core dilemma, as local excision carries a strikingly high local recurrence rate (up to 77%); neo-adjuvant imatinib is used to downsize tumors and facilitate sphincter preservation. Adjuvant imatinib must be given for a minimum of 3 years for high-risk disease. For Neuroendocrine Tumors (NETs), management is anatomical and metric: Rectal NETs < 1 cm can be cured endoscopically, while lesions > 2 cm require radical resection. For Colorectal Lymphoma, localized DLBCL is unique among GI malignancies, mandating upfront surgical resection followed by chemotherapy due to a clear survival advantage and the need to prevent catastrophic perforation from chemotherapy-induced tumor necrosis.