Rhabdomyosarcoma of head and neck varies in aggressiveness depending on the specific site of origin.

Objective: To evaluate predictive impact of granular subsites of head/neck rhabdomyosarcoma in a cross-age evaluation of the population-based SEER-program.

Methods: Data were obtained for cases 0-90+ years, newly diagnosed with rhabdomyosarcoma at head/neck, registered in SEER17 2000-2020. Disease-specific survival (DSS) and overall survival (OS) were the endpoints, using the Kaplan-Meier estimator and Cox proportional hazards regression model. A granular site categorization was established.

Results: Median age of 1114 cases was 11 years. 5-year OS and DSS were 59.1 %±3.1 (95 %CI) and 62.4 %±3.1 with median follow-up for 662 survivors of 8.6 years. Increasing age was independently associated with worse prognosis. The rate of affected subsites varied considerably. Age, histology, tumor size, disease stage, the proportion of pathologically examined and affected lymph nodes differed significantly according to granular subsite. Granular subsites were of independent predictive impact when adjusted for age, size, histology, stage, and pathological lymph node status. While rhabdomyosarcoma at orbit, parotid gland, and ear correlated with best survival, larynx, oral cavity, paranasal sinuses, brain, pharynx, and nose were associated with adverse survival. In contrast to all other subsites, nasal and paranasal sinus rhabdomyosarcoma were predominantly alveolar, large, distant spread, and with the highest proportion of affected lymph nodes. Rhabdomyosarcoma of nose/paranasal sinuses exhibit high potential of spreading not only suggesting different biology but thorough staging including pathological lymph node assessment.

Conclusions: Granular head/neck subsites show different characteristics between subsites and highly varying outcomes. Understanding the impact of granular head/neck subsites on outcome may inform risk-adapted and novel approaches to rhabdomyosarcoma.