An ovarian cyst is a fluid-filled sac that develops on or within an ovary. These sacs are extremely common, especially in women who are still having menstrual cycles. The vast majority of ovarian cysts are benign, meaning they are non-cancerous, and are frequently linked to the normal function of the reproductive system. While the fear that a cyst could become malignant is understandable, the risk of a typical ovarian cyst progressing to cancer is exceptionally low.
Common Ovarian Cysts and Their Behavior
Most ovarian cysts are classified as functional cysts, which are a direct result of the monthly menstrual cycle. These are not considered disease-related but indicate that the ovaries are functioning normally. Functional cysts include follicular cysts, which form when the follicle fails to rupture and release the egg, filling with fluid. Corpus luteum cysts form after ovulation when the sac that released the egg reseals and collects fluid or blood instead of shrinking.
These functional cysts are overwhelmingly benign and typically resolve on their own without medical intervention. Follicular cysts usually disappear within one to three months, while corpus luteum cysts often shrink within a few weeks. This spontaneous resolution differentiates them from growths that require more intensive management.
There are other types of benign cysts not tied to the menstrual cycle. These include dermoid cysts, which can contain various tissues like hair or fat, and endometriomas, often called “chocolate cysts,” caused by endometriosis. While these non-functional cysts may persist and sometimes require monitoring or surgical removal, they are overwhelmingly benign and do not transform into malignant tumors. Less than 1% of all ovarian cysts are cancerous, underscoring the low absolute risk.
Understanding the Risk of Malignancy
The question of whether a benign ovarian cyst can turn into cancer addresses a common misconception. Functional cysts, the most frequent type, do not evolve into cancer; there is no data supporting a connection between these common cysts and ovarian cancer. Ovarian cancer is generally understood to be a separate disease process that starts as a malignant growth.
Malignant tumors are structurally different from benign cysts from the outset. These cancerous masses often present as complex cysts or solid tumors. They are classified based on the cell type they originate from, such as epithelial, germ cell, or stromal cells. Cancerous lesions are much more likely to be found in postmenopausal women. Since the ovaries stop producing functional cysts after menopause, any newly detected cyst warrants closer evaluation.
A distinct category of growth is the borderline ovarian tumor, also known as a tumor of low malignant potential. These growths exhibit some cellular features of cancer but rarely spread aggressively beyond the ovary. They represent an intermediate category between clearly benign cysts and invasive ovarian cancer. While ovarian cysts are very common, ovarian cancer remains relatively rare, with approximately 20,000 people diagnosed each year in the United States.
Diagnostic Tools for Assessing Concern
When an ovarian mass is discovered, medical professionals use specific tools to determine if it is low-risk or potentially malignant. Transvaginal ultrasound is the primary diagnostic method, allowing doctors to visualize the cyst’s internal characteristics. A simple cyst, which is typically thin-walled and filled only with fluid, is highly likely to be benign and is often monitored with follow-up scans.
Conversely, a complex cyst displays features that raise concern for malignancy. These features include solid components, thick internal walls, or septations thicker than 3 millimeters. Color Doppler imaging is used with the ultrasound to check for blood flow within any solid components, as increased vascularity is a sign of potential malignancy. These visual characteristics are more predictive of cancer than size alone.
Another tool is the tumor marker CA-125, a protein often elevated in advanced ovarian cancer. This test is not used for general cancer screening because it has significant limitations. CA-125 levels can be elevated by numerous non-cancerous conditions, including menstruation, endometriosis, and uterine fibroids. In women who are still having periods, the level can vary widely, making it an unreliable standalone diagnostic test. CA-125 is usually ordered only when an ultrasound has identified a complex mass with suspicious features, and it is frequently used to monitor treatment response rather than to diagnose initially.
Management of an ovarian mass depends entirely on these diagnostic findings. Simple cysts that appear benign on ultrasound are usually managed with watchful waiting and a follow-up scan to confirm resolution. If the mass persists, grows, or displays concerning characteristics, management shifts toward surgical removal for a definitive pathological diagnosis.