Pathological response of salivary duct carcinoma to trastuzumab and docetaxel therapy

Role of HER2 in Prognosis of Salivary Duct Carcinoma: A Systematic Review and Meta-Analysis

OBJECTIVES

Salivary duct carcinoma (SDC) is a rare, aggressive malignancy with a poor prognosis. These tumors frequently stain positive for HER2/ErbB2, but data on the prognostic significance of HER2 status in SDC are mixed. We sought to determine whether HER2 status affects survival outcomes in SDC.

METHODS

PubMed, Embase, and Web of Science databases were searched from inception to October 2020. Eligibility was restricted to studies reporting HER2/ErbB2 overexpression in histologically confirmed de novo SDC or SDC ex pleomorphic adenoma, with corresponding overall (OS) and disease-free (DFS) survival measures. Separate multivariable and univariable meta-analyses were performed using random-effects models. Statistical heterogeneity was estimated by Cochran's Q and I² tests. Funnel plots were generated and Egger's test was used to assess for publication bias. The risk of bias was assessed with the Newcastle-Ottawa Scale.

RESULTS

Of 183 unique citations, 14 studies of 663 patients were included. Most included studies determined HER2 status according to ASCO/CAP guidelines. The univariable meta-analysis did not reveal an effect between HER2 status and OS (HR 1.09, 95% CI 0.84-1.42). In the multivariable analysis, HER2 positivity was associated with a HR of 1.49 for OS (95% CI 0.96-2.30). Fewer studies reported data for DFS than OS, with no relationship between HER2 status and DFS found on multivariable or univariable meta-analyses.

CONCLUSION

In patients with salivary duct carcinoma, HER2 positivity was not found to be associated with worse overall survival. This information may be useful when counseling patients and considering treatment options. Laryngoscope, 133:476-484, 2023.

ERBB2 amplification status in 67 salivary duct carcinomas assessed by immunohistochemistry, fluorescence in situ hybridization, and targeted exome sequencing

Salivary duct carcinoma (SDC) is an aggressive salivary gland malignancy with poor survival. Approximately 30% SDC harbor HER2 amplification and response to trastuzumab has been reported. However, a systematic approach for HER2 status assessment in this tumor type has not been established. A total of 67 tumor samples were evaluated for HER2 protein overexpression or ERBB2 gene amplification using at least 2 methods: immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and/or targeted exome next-generation sequencing (NGS). NGS assessed ERBB2 copy number fold change (FC) and total copy number (TCN). HER2 status was first determined by IHC/FISH according to the 2018 ASCO/CAP breast cancer guidelines. FISH results, the "gold standard", were compared with the NGS results. All (15/15) IHC positive, 35% (6/17) equivocal, and no (0/19) IHC negative SDC were HER2 amplified by FISH. HER2 FISH signal/cell showed a good correlation with FC (Spearman correlation: 0.708, R²: 0.501, p < 0.0001) and TCN (Spearman correlation: 0.763, R²: 0.582, p < 0.0001). Receiver operating characteristics curve estimation showed an area under curve (AUC) of 0.975 for ERBB2 FC. FC cutoff of ≥1.8 corresponded to an accuracy of 95.2% for ERBB2 amplification (Youden's index: 0.84, sensitivity: 89.47%, specificity: 100%). FC < 1.3 could be reliably classified as ERBB2 not amplified and FC ≥ 1.3 and <1.8 as equivocal. TCN estimation showed AUC of 0.981. TCN cutoff of >6.0 corresponded to an accuracy of 92% for HER2 amplification (Youden's index: 0.81, sensitivity: 81.2%, specificity: 100%). TCN < 4 could be reliably classified as ERBB2 not amplified and TCN ≥ 4.0 and ≤6.0 as equivocal. FC and TCN were binarized with respective cutoffs of ≥1.8 and ≥6.0 and the proportion of agreement with FISH were 95% and 92%, respectively. The assessment of ERBB2 copy number by NGS is accurate and reliable with FC or TCN nearly equivalent to FISH in identifying HER2 amplified SDC.

Systemic therapy in the management of recurrent or metastatic salivary duct carcinoma: A systematic review

BACKGROUND

Salivary duct carcinoma (SDC) is an aggressive subtype of salivary gland cancer. Approximately half of SDC patients will develop recurrences or metastases. Therapeutic palliative therapy is therefore often needed. The majority of SDC tumors expresses the androgen receptor (AR) and one-third expresses human epidermal growth factor receptor 2 (HER2), both are potential therapeutic targets. The aim of this paper is to systematically review and summarize the evidence on systemic palliative therapy for SDC and to provide treatment recommendations.

MATERIALS AND METHODS

Electronic libraries were systematically searched with a broad search strategy to identify studies where SDC patients received systemic therapy. Due to the rarity of SDC no restrictions were placed on study designs.

RESULTS

The search resulted in 2014 articles of which 153 were full-text analyzed. Forty-five studies were included in the analysis, which included in total 256 SDC patients receiving systemic therapy. Two phase 2 trials primarily including SDC patients were identified. The majority of the studies were case series or case reports, resulting in an overall low quality of available evidence. Based on studies including ≥ 5 SDC patients, objective responses to HER2 targeting agents were observed in 60-70%, to AR pathway agents in 18-53% and to chemotherapy in 10-50%.

CONCLUSION

For AR or HER2 positive SDC, agents targeting these pathways are the cornerstone for palliative treatment. Regarding chemotherapy, the combination of carboplatin combined with a taxane is best studied. Regarding other targeted agents and immunotherapy evidence is anecdotal, limiting formulation of treatment recommendations for these antineoplastic agents.