Adenoid cystic carcinoma (ACC) is an uncommon cancer that most often develops in the salivary glands or other areas of the head and neck. It grows slowly, sometimes over years, but has a deceptive tendency to spread along nerves and eventually metastasize to distant organs. That combination of slow growth and long-term persistence makes ACC different from most other cancers and creates unique challenges for treatment and monitoring.
Where ACC Develops
The salivary glands are the most common starting point, but ACC can form in a surprisingly wide range of tissues. It also arises in the tear (lacrimal) glands, sweat glands, skin, breast tissue, cervix, prostate, and the lining of the respiratory tract. What these sites share is glandular tissue capable of producing secretions, which is the cell type ACC originates from.
When ACC appears in the breast, it belongs to the triple-negative subtype, meaning the tumor cells lack the three receptors (estrogen, progesterone, and HER2) that many breast cancers rely on for growth. Interestingly, breast ACC tends to behave less aggressively than salivary gland ACC, despite looking nearly identical under a microscope. Salivary and lacrimal gland tumors carry a more concerning long-term outlook, with 10-year disease-specific survival rates around 75% and 52%, respectively.
How It Looks Under a Microscope
Pathologists classify ACC into three growth patterns, and which one dominates has a real effect on prognosis.
- Cribriform: The most common pattern. Tumor cells form nests with small cyst-like spaces scattered throughout, giving a Swiss cheese appearance.
- Tubular: Cells arrange into small tube-shaped structures with a central channel. Like the cribriform pattern, this type tends to grow slowly and behave less aggressively.
- Solid: Dense sheets of cells without the characteristic holes or tubes. This pattern is considered high grade, with higher rates of recurrence and poorer survival compared to the other two types.
Most ACC tumors contain a mix of these patterns. The overall grade is typically determined by how much solid growth is present. A tumor that is predominantly cribriform or tubular carries a better prognosis than one with a significant solid component, which tends to grow faster and spread more readily.
The Defining Feature: Nerve Invasion
What sets ACC apart from most other cancers is its remarkable ability to invade nerves. In the majority of ACC cases, cancer cells creep into the nerve fibers surrounding the tumor, sometimes traveling long distances along nerve pathways. This happens on such a microscopic level that it can be invisible on imaging scans and difficult to detect even during surgery.
This nerve-tracking behavior, called perineural invasion, has two major consequences. First, it can cause pain, numbness, tingling, or weakness in the areas those nerves supply, sometimes before a tumor is even detected. In head and neck ACC, facial pain or paralysis may be an early sign. Second, it makes surgical cure extremely difficult. Tumor cells can extend far beyond the visible edges of the mass, following nerve branches toward the base of the skull or other critical structures. Surgeons often face a difficult tradeoff between removing enough tissue to capture all the cancer and preserving function in nearby nerves.
Symptoms
Because ACC grows slowly, early symptoms are often subtle and easy to dismiss. A painless lump in the mouth, under the jaw, or near the ear is the most common first sign when the salivary glands are involved. As the tumor grows or begins invading nerves, symptoms become more noticeable: persistent pain in the face or mouth, numbness or tingling, difficulty swallowing, or changes in facial movement. In other locations, symptoms depend on the organ involved, such as a breast lump, a nasal obstruction, or skin nodule.
The slow pace of growth means some people live with mild symptoms for months or even years before receiving a diagnosis, which can allow the cancer more time to extend along nerve pathways.
What Drives ACC at the Genetic Level
A key genetic event in many ACC tumors is a rearrangement between chromosomes 6 and 9, which fuses two genes together. The resulting fusion gene drives overproduction of a protein that promotes cancer cell growth. This fusion has been detected in about 28% of primary tumors and 35% of metastatic cases, and it appears more frequently in patients over age 50. While not present in every ACC tumor, this genetic signature is distinctive enough that it is not found in other types of salivary gland cancer, making it a useful marker for confirming a diagnosis.
Treatment Approach
Surgery is the primary treatment for ACC. The goal is to remove the tumor with clear margins, meaning no cancer cells at the edges of the removed tissue. In practice, this is often harder than it sounds. The tendency of ACC to spread microscopically along nerves means that what appears to be a clean resection may still leave behind invisible trails of cancer cells. Surgeons sometimes face the choice between an extremely wide resection, which can damage important nerves and structures, or a more conservative removal followed by radiation.
ACC is considered sensitive to radiation, which is why radiation therapy frequently follows surgery. It targets the tissue surrounding the surgical site, including nerve pathways where microscopic disease may remain. For tumors that cannot be fully removed, or in cases where perineural spread has been identified, radiation plays an especially important role in treatment planning. The radiation fields are carefully designed to cover the nerve routes the tumor may have followed.
Recurrence and Metastasis
One of the most challenging aspects of ACC is its tendency to come back. Most people with ACC will experience a recurrence within 5 to 10 years, and the local recurrence rate is approximately 40% at 5 years. This long timeline is unusual in oncology and means that even patients who appear cancer-free need many years of follow-up surveillance.
Distant metastasis eventually occurs in roughly 40% of patients. The lungs are the most common site by far, accounting for about 70% of distant spread. Bone, brain, and liver are the next most frequent locations. Notably, ACC does not typically spread to lymph nodes the way many other cancers do. Only about 5% to 10% of cases involve lymph node metastasis.
Distant metastases can appear even after the primary tumor has been successfully controlled, sometimes emerging many years later. In one study, distant spread was identified in 45% of patients during follow-up, at an average of over 8 years after initial treatment. This delayed pattern is part of what makes ACC so unpredictable. A patient can be disease-free for years, only to discover metastatic disease a decade or more down the line.
Living With a Slow but Persistent Cancer
The paradox of ACC is that its slow growth means many people live for years, even with metastatic disease, but it also means the cancer rarely goes away entirely. Five-year survival rates can appear relatively favorable compared to more aggressive cancers, but 10- and 15-year numbers tell a more sobering story as recurrences accumulate over time. For salivary gland ACC, the 10-year disease-specific survival is around 75%, which is significantly lower than the 5-year figures suggest.
Because of the long time horizon, ongoing monitoring with imaging, typically of the lungs and original tumor site, continues for many years after treatment. People living with ACC often describe it as a cancer you manage over a lifetime rather than one you fight in a single battle.
Newer Treatment Options
Standard chemotherapy has shown limited effectiveness against ACC, which has driven interest in more targeted approaches. One active area of investigation involves antibody-drug conjugates, which are engineered molecules that attach to specific proteins on cancer cells and deliver a toxic payload directly to them. A phase II clinical trial through the National Cancer Institute is currently testing one such drug in patients with recurrent or metastatic ACC. The drug targets a protein called nectin-4 on the surface of cancer cells, delivering a cell-killing agent precisely where it is needed while sparing healthy tissue.
The genetic fusion driving many ACC tumors also represents a potential therapeutic target. Because the fusion gene causes overproduction of a growth-promoting protein, blocking that pathway could slow tumor progression. These targeted strategies are still being evaluated in clinical trials, and patients with recurrent or metastatic ACC may want to explore whether any active trials are a good fit for their situation through resources like the National Cancer Institute’s trial search tool.