Rare subtypes of gastroesophageal malignancies represent a small but biologically meaningful fraction of upper gastrointestinal cancers. Although most therapeutic algorithms are derived from conventional squamous cell carcinoma and adenocarcinoma, uncommon entities such as variants of squamous cell carcinoma, lymphoepithelioma-like carcinoma, adenosquamous carcinoma, neuroendocrine carcinoma, and others display distinct clinicopathologic, immunologic, and molecular features that may influence prognosis and therapeutic decision-making. This review synthesizes current evidence regarding the epidemiology, histopathology, molecular alterations, and emerging therapeutic vulnerabilities across these rare subtypes. Importantly, these tumors frequently exhibit aggressive clinical behavior and are often managed by extrapolation from more common histologies due to the absence of prospective data. Increasing integration of genomic profiling, immune characterization, and biomarker-driven stratification is essential to refine diagnoses, expand precision therapeutic strategies, and improve outcomes. Recognition of these rare subtypes in routine practice is critical, as even small molecularly defined populations may carry disproportionate biological and translational significance within oncology.