Incurable advanced salivary gland tumours: a retrospective analysis and peek into the perplexing clinical and molecular intricacies from a tertiary care centre in India

BACKGROUND: Salivary gland tumours are rare cancers with variable course and prognosis. There is a paucity of data, especially for the advanced stages. MATERIALS AND METHODS: This is a retrospective analysis carried out in our institute. All patients seeking treatment for incurable advanced salivary gland tumours from October 2018 to September 2022 were included. Relevant clinical data were collected and appropriate statistical analysis was applied. RESULTS: 30 patients were included in the analysis. The parotid gland was the most common site of origin (73%). Adenoid cystic carcinoma (ACC) and salivary duct carcinoma (SDC) were equally (37%) the most common pathological subtypes. The majority of patients were males (73%) and lungs (57%) were the most common site of metastases. On molecular analysis, SDC had high rates of androgen receptor (AR) (90%) and human epidermal growth factor receptor 2 (HER2) (55%) positivity. Mucoepidermoid carcinoma (MEC) had AR and HER2 positivity rates of 17% and 20%, respectively, while for ACC it was even lower. A variety of treatment regimens including hormonal therapy, anti-HER2 targeted therapy and chemotherapy were used in first-line treatment. With an overall response rate (ORR) of 10/21 (48%), only 9/21 (43%) went on to receive second-line treatment with an ORR of 4/9 (44%). The progression-free survival (PFS) with first-line treatment (PFS1) was a median of 5 months. The median PFS1 was worst for MEC. The median overall survival (OS) was 10 months. Median OS for ACC, SDC and MEC were 11, 10 and 7 months, respectively. At 24 months, ACC had much higher survival (50%) than others (10%) indicating a proportion of ACC with an indolent course. CONCLUSION: Our analysis highlights the variable disease biology of advanced salivary gland tumours and throws light on the various possible treatment targets and strategies. Molecular profiling and advancement in targeted therapies are expected to increase survival in this group of rare cancers.