Clear cell carcinoma is a type of cancer named for the way its cells look under a microscope: pale, almost transparent, as if the inside has been washed out. That distinctive appearance comes from abnormal buildup of sugars (glycogen) or fats inside the tumor cells, which dissolve during standard lab processing and leave behind an empty, glassy look. Clear cell carcinoma most commonly arises in the kidneys, where it accounts for roughly 70% of all kidney cancers, but it also develops in the ovaries, uterus, and less frequently in organs like the lung, bladder, and thyroid.
Why the Cells Look “Clear”
Under normal conditions, cells contain a balanced mix of proteins, fats, and stored sugars. In clear cell carcinoma, something goes wrong with the cell’s metabolism, causing it to hoard glycogen or lipids in large quantities. When a pathologist prepares a tissue sample on a slide, the chemicals used in processing dissolve those stored substances. What’s left is a cell with a large, empty-looking interior and a visible outer border, giving the tumor its name.
This isn’t just a cosmetic quirk. The metabolic shift behind it reflects deeper genetic damage that drives the cancer’s growth and, in some locations, makes it behave differently from other tumor types.
Clear Cell Renal Cell Carcinoma
The kidney is by far the most common site. Clear cell renal cell carcinoma (ccRCC) makes up about 70% of all kidney cancers, making it the dominant subtype. The other main kidney cancer types, papillary and chromophobe, are considerably less common.
A key genetic event in ccRCC involves a stretch of chromosome 3. Studies find that roughly 93% of clear cell kidney tumors show a loss of genetic material on the short arm of chromosome 3, a region that houses a tumor-suppressing gene called VHL. When VHL is knocked out through mutation, deletion, or chemical silencing, cells lose an important brake on growth and blood vessel formation. About 75% of ccRCC tumors carry both the chromosome 3 loss and a direct VHL alteration.
This genetic fingerprint matters because VHL normally helps cells sense oxygen levels and control the signals that trigger new blood vessel growth. Without it, tumors ramp up blood supply to feed themselves. That vulnerability is exactly what some modern treatments exploit.
Symptoms and How It’s Found
Kidney cancer is often silent in its early stages. Between 25% and 30% of people with renal cell carcinoma have no symptoms at all, and their cancer is discovered incidentally on an imaging scan done for another reason. When symptoms do appear, the most common ones are blood in the urine (about 40% of cases), flank pain (40%), and a mass that can be felt in the side or abdomen (25%). All three occurring together is actually uncommon.
Survival by Stage
Prognosis depends heavily on how far the cancer has spread at diagnosis. Based on data from people diagnosed between 2015 and 2021, the five-year relative survival rate for kidney cancer that remains confined to the kidney (localized) is 93%. When it has spread to nearby tissues or lymph nodes (regional), the rate drops to 76%. For cancer that has reached distant organs, the five-year survival falls to 19%. Across all stages combined, the overall five-year survival rate is 79%, reflecting the fact that many kidney cancers are caught early.
Treatment for Advanced Disease
Early-stage ccRCC is typically treated with surgery to remove part or all of the affected kidney. For advanced or metastatic disease, treatment has shifted dramatically in recent years toward combinations of immunotherapy and drugs that block blood vessel growth.
These combination approaches pair immune checkpoint inhibitors, which help the immune system recognize and attack cancer cells, with drugs that cut off the tumor’s blood supply. For patients with intermediate or high-risk advanced disease, dual immunotherapy regimens became a standard first-line option after clinical trials showed significant improvements in survival compared to older single-drug approaches. Other combinations pair an immune checkpoint inhibitor with a blood-vessel-blocking pill, and several of these have also shown improved outcomes in large trials. Your oncologist selects among these options based on the cancer’s risk profile and your overall health.
Ovarian Clear Cell Carcinoma
Clear cell carcinoma of the ovary (OCCC) is less common than the high-grade serous type that makes up the majority of ovarian cancers, but it behaves quite differently and carries distinct challenges.
The strongest known risk factor is endometriosis. Between 50% and 74% of ovarian clear cell carcinoma cases are associated with endometriosis, and women with endometriosis face roughly three times the risk of developing this specific subtype compared to women without it. Endometriosis is considered a precancerous condition for OCCC, with the chronic inflammation and cellular changes in endometriotic tissue believed to create an environment where cancerous transformation can occur over time.
One of the most clinically significant features of OCCC is its resistance to standard platinum-based chemotherapy. Response rates to first-line platinum regimens range from only 11% to 56%, a stark contrast to high-grade serous ovarian cancer, where more than 80% of tumors respond to the same drugs. This resistance means that when OCCC is diagnosed at an advanced stage, prognosis tends to be worse than for other ovarian cancer subtypes. Early-stage OCCC, however, has a more favorable outlook, particularly when the tumor can be completely removed surgically.
Other Sites Where Clear Cell Carcinoma Occurs
Beyond the kidney and ovary, clear cell carcinoma can arise in the uterus (endometrium), where it is considered an aggressive subtype that accounts for a small percentage of endometrial cancers. It can also develop in the vagina, cervix, lung, liver, bladder, and thyroid, though these are rare. In each location, the characteristic transparent cell appearance is the defining feature under the microscope, but the genetic drivers, behavior, and treatment approaches vary depending on the organ involved.
In the breast, a very rare variant called glycogen-rich clear cell carcinoma is classified separately. To earn this diagnosis, more than 90% of the tumor cells must contain glycogen that stains positive with a specific lab test. Its rarity makes large studies difficult, and treatment generally follows standard breast cancer protocols.
How It’s Diagnosed
Diagnosis requires a tissue biopsy examined under a microscope. The transparent cell appearance raises initial suspicion, but pathologists use additional staining techniques to confirm the subtype and rule out look-alikes. In the kidney, tumor cells typically stain positive for specific protein markers on their surface. In ovarian cases, genetic analysis often reveals mutations in a gene called ARID1A, found in 46% to 57% of tumors, which helps distinguish clear cell carcinoma from other ovarian cancer types.
Imaging studies like CT scans, MRIs, or ultrasounds help identify the tumor’s size and whether it has spread, but the microscopic examination of tissue is what ultimately determines whether a cancer is the clear cell type. This distinction matters because it directly influences treatment decisions and expected outcomes.