Post-operative radiotherapy in adenoid cystic carcinoma of salivary glands versus surgery alone: what is the evidence about survival and local control? A systematic review and meta-analysis

BACKGROUND

Adenoid cystic carcinoma of the salivary glands is a relatively rare malignancy characterized by slow growth and a poor prognosis, and effective treatments remain challenging to identify. This systematic review, following the PRISMA guidelines, aimed to analyze the potential benefits of post-operative radiotherapy in terms of local control of recurrences and survival advantages when compared with surgery alone in patients with adenoid cystic carcinoma.

METHODS

A comprehensive systematic review was conducted by searching the MEDLINE, Cochrane, EMBASE, and OVID databases from January 1999 to July 2022. The goal was to identify articles comparing surgery alone with surgery plus postoperative radiotherapy for adenoid cystic carcinoma of the salivary glands. Downs and Black Checklist was used to assess the methodological quality and risk of bias of each included study. The data analysis was performed using Review Manager version 5.4.1.

RESULTS

This review included 8 studies comprising a total of 3103 patients, divided based on the analyzed outcomes. The pooled odds ratio for overall survival at 5 years was 0.87 (95% confidence interval 0.43-1.76, p = 0.70), and at 10 years was 1.23 (95% confidence interval 0.69-2.16, p = 0.48). In both cases, no statistically significant differences were observed. However, the pooled odds ratio for local control at 5 years was 3.37 (95% confidence interval 1.35-8.42, p = 0.009), providing strong support for the use of post-operative radiation.

CONCLUSIONS

The findings from the meta-analysis suggest that post-operative radiotherapy significantly improves local control in patients with adenoid cystic carcinoma. However, there was no statistically significant increase in survival at 5 and 10 years. It is essential to note that the quality of the studies included in this meta-analysis ranged from fair to poor. To better clarify the indications for post-operative radiotherapy, future high-quality research is needed, particularly with improved stratification of patient groups. Additionally, it is important to recognize that achieving local control in adenoid cystic carcinoma is crucial for enhancing the overall quality of life for patients. We acknowledge that this review was not registered in the PROSPERO database, and the data pooling was conducted using a random effects model.

Approaches to the Management of Metastatic Adenoid Cystic Carcinoma

High rates of recurrence and distant metastasis are a foremost challenge in the management of adenoid cystic carcinoma (ACC), occurring in approximately 40% of all ACC patients. Despite the morbidity and mortality resulting from recurrent/metastatic (R/M) disease, there are no FDA-approved systemic agents for these patients. In this review, we summarize pertinent ACC pathophysiology and its implications for different systemic treatment regimens in R/M ACC. We review the evidence for the most widely used systemic agents - cytotoxic chemotherapy and tyrosine kinase inhibitors (TKIs) targeting VEGFR - in addition to immune checkpoint inhibitors and non-TKI biologic agents. Exciting emerging targets for R/M ACC, including inhibitors of Notch signaling, stemness, PRMT5, and Axl, are also discussed. Lastly, we review local therapies for small-volume lung disease in patients with oligometastatic ACC, specifically pulmonary metastasectomy and stereotactic body radiation therapy (SBRT). Future development of targeted molecular agents which exploit the underlying biology of this disease may yield novel therapeutic options to improve clinical outcomes in patients with R/M ACC.

Mortality risk after clinical management of recurrent and metastatic adenoid cystic carcinoma

Background

Management of locoregional recurrence (LRR) and distant metastasis (DM) in adenoid cystic carcinoma (ACC) is guided by limited data. We investigated mortality risks in patients diagnosed and treated for recurrent ACC.

Methods

A retrospective review of ACC patients treated from 1989 to 2016 identified 36 patients with LRR or DM. High-risk disease was defined as skull base involvement (for LRR) or International Registry of Lung Metastases Group III/IV or extrapulmonary site of metastasis (for DM). Kaplan-Meier method, log-rank tests, and Cox proportional hazards were used for time-to-event analysis.

Results

Among 20 LRR and 16 DM patients, the median times to recurrence were 51 and 50 months, respectively. The median follow-up post-recurrence was 37.5 months (interquartile range (IQR)16.5–56.5). Post-recurrence 3-year overall survival (OS) was 78.5%, 73.3% for LRR and 85.1% for DM (p = 0.62). High-risk recurrences were associated with worse 3-year OS (68.8% for high-risk and 92.3% for low-risk, χ2 = 10.4, p = 0.001).

Among LRR patients, 90% had surgery as part of their treatment. Multimodality therapy, age, and histopathologic features (size, margins, solid histology, lymphovascular or perineural invasion) were not associated with PFS or OS. High-risk LRR was the only variable associated with OS (χ2 = 5.9, p = 0.01).

Among DM patients, six were initially managed with observation and ten received surgery, RT, or systemic therapy. Upfront therapy was not associated with improved PFS or OS. High-risk DM was the only variable associated with OS (χ2 = 4.7, p = 0.03).

Conclusions

High-risk LRR and DM were associated with decreased 3-year OS. More effective therapies are needed for high-risk ACC recurrences.

Local ablative treatments of oligometastases from head and neck carcinomas

BACKGROUND

Median survival for recurrent/metastatic (unknown poly/oligometastatic status) head and neck cancer patients (HNSCC) is ten months with best systemic treatment. Metastatic ablation shows promising results in selected patients with several tumor types. We aimed to assess the role of surgery and stereotactic ablative body radiotherapy (SABR) with respect to survival in HNSCC.

MATERIALS AND METHODS

Published data on metastatic HNSCC treated ablatively were analyzed.

RESULTS

Five-year survival rates after pulmonary/liver metastasectomy exceed 20% in selected patients. Two-year survival after lung SABRT of metastasectomy yields 35%. Interesting data on survival and tolerance are reported in other metastatic sites.

CONCLUSION

Surgery yields the best level of evidence. However, non-invasive SABR is efficient and well-tolerated in lung/liver, bone and other metastatic locations. Systemic treatment may be given sequentially with ablative treatments, or omitted in well-identified situations. Proper patient selection for local ablative treatment and optimal therapeutic sequence should be assessed in randomized trials.

Salivary gland adenoid cystic carcinoma with cervical lymph node metastasis: a preliminary study of 62 cases

Adenoid cystic carcinoma (ACC) is an infrequent malignant neoplasm that originates most commonly in the major and minor salivary glands of the head and neck region. This study provides new information on head and neck ACC with cervical lymph node metastasis. Of 616 patients who underwent primary tumour resection from 1995 to 2008 in the authors' hospital, 62 cases with cervical lymph node metastasis were analyzed. The general incidence of cervical lymph node metastasis in ACC was approximately 10%. The base of tongue, mobile tongue and mouth floor were the most frequent sites of lymph nodes metastasis, with incidences of 19.2%, 17.6% and 15.3%, respectively. Most cases occurred via a classic 'tunnel-style' metastasis and the level Ib and II regions were the most frequently involved. Primary site and lymphovascular invasion were significantly associated with lymph node metastasis. High patient mortality was significantly correlated with lymph node positive cases. The tongue-mouth floor complex has a high propensity for cervical lymph node metastasis, which occurs through a classic 'tunnel-style' metastasis. Peritumoral lymphovascular invasion could be taken as strong predictor for lymph node metastasis, which ultimately leads to poor prognosis of ACC patient. Selective neck dissection should be considered in such cases.

Clinicopathological factors are predictors of distant metastasis from major salivary gland carcinomas

The risk of distant metastasis of salivary gland cancers has usually been associated with histological type, tumour size, and site. The aim of this study was to evaluate a series of patients with major salivary gland carcinomas in order to identify potential risk factors associated with distant metastasis. 255 patients treated for major salivary gland carcinoma in Brazil from 1953 to 2004 were reviewed. Clinical and treatment data were obtained from the medical records and histological features reviewed. 57 (22%) of 255 patients had distant metastasis. The lungs were the most common metastatic site (40 cases, 65%) and adenoid cystic carcinoma the most frequent histological type involved (27 cases, 47%). The percentage of tumours in the submandibular, parotid, and sublingual glands that presented distant metastasis was 42%, 20%, and 17%, respectively. These results provide evidences that clinicopathological factors (tumour site and histology) are significant predictors of distant metastasis in patients with major salivary gland carcinomas.