The Impact of Comorbidity on Severe Procedure-Coded Inpatient Events in Head and Neck Cancer and Thyroid Cancer Hospitalizations in Germany: A Nationwide DRG Analysis, 2005–2021

Background: Comorbidity is an important determinant of treatment selection and in-hospital complications in patients with head and neck cancer (HNC) and thyroid cancer (TC), yet population-based evidence on this relationship remains limited. Methods: We analyzed nationwide Diagnosis-Related Groups (DRG) data from 1,552,028 inpatient HNC and TC treatments of patients aged ≥30 years in Germany between 2005 and 2021. The aim was to characterize the association of comorbidity and severe treatment-related procedure-coded inpatient events (IEs) with gender, age, tumor subsite, and treatment type. Results: The largest proportion of treatments occurred in patients aged 60–69 years (33.5%). The most frequent tumor subsites were the oropharynx, thyroid gland, oral cavity, larynx, and hypopharynx, with 35.52, 33.84, 33.60, 26.12, and 15.76 treatments per 100,000 population per year, respectively. Overall, 38% of cases had a Charlson Comorbidity Index (CCI) ≥ 1, with the highest mean CCI observed for C14 (other sites of the lip, oral cavity and pharynx) and C12 (piriform sinus). IEs requiring additional in-hospital treatment occurred in 19.3% of cases. After adjustment for age, tumor location, and treatment type, men had a lower risk of IEs than women (OR 0.929; CI 0.919–0.939; p < 0.001). Increasing comorbidity was associated with a higher IE risk, reaching a plateau at CCI ≥ 4 (OR 2.135; CI 2.029–2.246; p < 0.001). IE risk was high during chemotherapy/immunotherapy (OR 29.527; CI 28.897–30.170; p < 0.001), followed by surgery (OR 3.465; CI 3.433–3.498; p < 0.001), whereas radiotherapy showed the lowest risk (OR 1.339; CI 1.313–1.366; p < 0.001). Conclusions: These findings highlight substantial heterogeneity in comorbidity and IE risk among patients with HNC or TC.