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Adenoid Cystic Carcinoma

Also known as ACC, Adenoid cystic carcinoma is a form of malignant neoplasm that arises within secretory glands.Other sites of origin include the trachea, lacrimal gland, breast, skin, and vulva. This neoplasm is defined by its distinctive histologic appearance. ACC may also arise in other primary sites, such as the skin, the neck of the uterus (cervix) in females; the prostate gland in males; and even other areas.

ACC tumors are characterized by a distinctive pattern in which abnormal "nests" or cords of certain cells (epithelial cells) surround and/or infiltrate ducts or glandular structures within the affected organ. These structures are typically filled with a mucous-like material or contain abnormal fibrous membranes (hyaline membranes). Such characteristics are apparent during microscopic evaluation of the tumor cells. ACC is considered a low-grade malignancy that has a history of slow growth, but tends to be aggressively invasive and to infiltrate nearby lymph nodes as well as the "sheaths" or coatings surrounding nerve fibers (perineural spaces). This form of cancer may have a tendency to recur later at the site where it first developed (local recurrence) and to spread to distant bodily sites, particularly the lungs, potentially resulting in life-threatening complications.

One of the most frustrating things in dealing with ACC is the impact of distant metastasis, which can be frustratingly frequent and seen in 25% to 50% of cases. Because this tumor invades nerves, it also has propensity for intravascular and perivascular growth, which presumably leads to hematogenous spread. This occurs in an unpredictable manner. Distant mets can develop despite local regional control and can occur more than ten years after the initial therapy. Not surprisingly, these patients do not do as well but the mean survival after onset can be greater than five years. The lungs are the most common site, but distant mets can also be seen in the brain, liver and bone. Distant metastasis is more common with solid tumors.

The most important study that focused just on distant metastasis was from Spiro from Sloan-Kettering. This looked at 196 patients treated there over 40 years. They found that 62% had some form of treatment failure and one-third had distant metastasis (DM). Of those 74 patients with DM, 51 were associated with locoregional recurrence but in 23, DM was the only kind of treatment failure. The lungs were the most common site. Half of these patients survived 3 years but 10% survived as long as 10 years. He found that survival was influenced by the tumor size and the presence of locoregional recurrence. This study highlights some important points. The most important one is these patients need to be followed for decades. The classic five year survival period is really not adequate with adenoid cystic carcinoma. He also found that the pulmonary mets were rarely solitary. Over time the normal lung parenchyma is replaced by confluent metastatic disease. These patients can do fairly well and are usually asymptomatic until late in their clinical course. Once symptoms develop, survival is usually less than two years. Another important thing to consider when reviewing studies that encompass patients treated over four decades is that treatment in the 1940's differed from treatment in the 1980's. Clearly, patients in the latter half of their study had a more liberal use of postoperative radiation but they found there was no change in the rate of DM with the use of post-operative XRT. Not surprising, larger tumors had a greater chance of distant metastases, but it was unclear why patients developed DM without any other signs of treatment failure. High tumor grade was suggestive but not statistically significant. They recommended chemotherapy really only to palliate symptoms.

Chemotherapy has a limited, poorly defined role with ACC. There have been studies that have shown cisplatin, 5-fluoruracil, doxorubicin, and cyclophosphamide, have some activity, either as single agents or in combination. There are reports of some successes and remissions. Chemotherapy treatment protocols really offer no statistically significant differences in disease free survival when compared to well matched historic controls.