Distant metastasis in adenoid cystic carcinoma of salivary origin

Adenoid cystic carcinoma (ACC) is an aggressive, often indolent tumor, with a high incidence of distant metastasis (DM). Relatively little has been written about the factors that influence distant spread and subsequent survival because it is uncommon and more than a decade of observation may be required to appreciate the prolonged clinical course in some patients.

We have retrospectively studied 196 determinate patients who received definitive treatment in our hospital between 1939 and 1986 for ACC in all salivary sites. Inclusion criteria were no prior treatment elsewhere other than excisional biopsy and eligibility for follow-up of at least 10 years. Variables assessed for their impact on distant metastasis included age, gender, site, size, node status, stage, grade, and locoregional treatment failure.

Treatment failure occurred in a total of 122 of 196 determinate patients (62%), 74 of whom had DM (38%). This was usually associated with locoregional recurrence (51 patients), but DM was the only indication of failure in 23 whose primary tumor was controlled. Of the 74 patients with known DM, the lung was recorded as the only involved site in 50 patients, lung was involved in addition to other sites in 17, bone metastases alone occured in 5, and the remaining 2 developed disseminated disease. Disease-free intervals varied from 1 month to 19 years (median 36 months) and exceeded 10 years in 9 of 113 patients (8%) with adequate information about treatment failure. Survival with DM was less than 3 years in 54%, but more than 10 yrs in 10% (maximum 16 years). The only significant factors influencing survival were the size of the primary tumor (P <0.0000), local or neck recurrence (P = 0.0006), and the presence of nodal involvement (P = 0.02).

The high incidence of DM with locoregional failure confirms the importance of aggressive initial surgery, combined with irradiation, for high-stage tumors or involved surgical margins. Large tumor size and lymph node involvement, rather than microscopic appearance, were predictive of DM. Considering that lung metastases are usually multiple, and prolonged survival without treatment is not unusual, resection of pulmonary metastases may be hard to justify in ACC patients based on the limited experience thus far reported. Chemotherapy for metastatic ACC is probably best withheld until symptoms appear.