Ordinal sentiment classification in cancer support forums: a controlled benchmark of machine learning and transformer models.

Introduction: Online cancer support forums contain naturalistic accounts of fear, uncertainty, coping, and caregiver strain. Such text may contribute to digital phenotyping as one component of longitudinal, human-supervised monitoring, but the operational link between psychosocial distress and sentiment labels requires explicit evaluation. Methods: We benchmarked representative classical, recurrent, and transformer-based models for four-class ordinal sentiment classification using the Mental Health Insights-Vulnerable Cancer Patients dataset (N = 10,392). Models were evaluated under a single validation-guided 60/20/20 holdout split using weighted F1, macro one-vs-rest AUC, class-specific performance, and paired comparisons. Results: Transformer models achieved the strongest overall performance. ALBERT produced the highest weighted F1 and macro AUC (0.7667 and 0.931, respectively), while BioBERT was closely comparable (weighted F1 = 0.7613; macro AUC = 0.917) and showed slightly higher recall for the "very negative" class (0.8019 vs. 0.7736). Error analysis showed that transformer errors concentrated around ordinal decision boundaries, while residual positive-class errors remained operationally important for supportive workflows. Discussion: These split-specific findings support transformer fine-tuning as a decision-support component for vulnerability-oriented monitoring, while emphasizing calibration, transparent error review, and human oversight rather than autonomous clinical assessment.