What Is a Pelvic Tumor? Symptoms, Causes, and Diagnosis

A pelvic tumor is any abnormal growth of tissue within the pelvis, the bowl-shaped bony structure at the base of your torso that houses the bladder, rectum, and reproductive organs. These tumors can be benign (noncancerous) or malignant (cancerous), and most of them originate in the gastrointestinal or genitourinary organs, though some arise from bone, connective tissue, nerves, or blood vessels in the region.¹ Because so many different organs are packed into a relatively small space, the word “pelvic tumor” is less a single diagnosis than an umbrella covering dozens of possible conditions, each with its own behavior, prognosis, and treatment path.

Why the Pelvis Is a Common Site for Tumors

The pelvis contains organs from three major body systems: the digestive tract (rectum, sigmoid colon), the urinary system (bladder, ureters, urethra), and the reproductive system (uterus, ovaries, and fallopian tubes in women; prostate and seminal vesicles in men). Each of these organs can independently develop tumors. On top of that, the pelvis is lined with muscles, nerves, fat, and connective tissue that can also give rise to growths. The pelvic bones themselves can develop primary bone tumors, though these are far less common than soft-tissue or organ-based ones.

Because so many tissue types converge in one area, a pelvic tumor discovered on imaging could be almost anything. The challenge for clinicians is figuring out which organ or tissue type the mass comes from, whether it is benign or malignant, and how far it extends. That determination drives every treatment decision.

Benign Versus Malignant Pelvic Tumors

Not every pelvic mass is cancer. In fact, many pelvic tumors turn out to be benign. Uterine leiomyomas (fibroids) are the most common benign tumors of the uterus, and many women live with them for years without knowing.² Ovarian cysts are another frequent finding, often discovered incidentally during imaging done for unrelated reasons.³ Other benign pelvic growths include endometriomas (cysts from endometriosis), dermoid cysts, and solitary fibrous tumors.

Malignant pelvic tumors include cancers of the cervix, ovary, uterus, bladder, prostate, rectum, and anus, along with rarer sarcomas of the bone and soft tissue. The clinical challenge is that benign and malignant masses can look similar on imaging, especially when a benign mass is large or has undergone degenerative changes. Researchers have developed scoring systems that combine factors like patient age, ultrasound features, and blood-marker levels to estimate the likelihood a pelvic mass is cancerous. In studies comparing these systems, malignant masses tended to appear in older patients and showed higher levels of the blood marker CA-125, along with distinct ultrasound characteristics such as lower resistance to blood flow.⁴

Common Types of Pelvic Tumors

Gynecological Tumors

In women, the most frequently encountered pelvic tumors involve the uterus or ovaries. Uterine fibroids are overwhelmingly benign, but they can occasionally be confused on imaging with uterine leiomyosarcoma, a rare but aggressive cancer. The confusion arises because large or degenerating fibroids can look similar on MRI to leiomyosarcomas.² Reassuringly, molecular research suggests the two tumors have separate developmental pathways, and fewer than one in 500 leiomyosarcomas arise within a pre-existing fibroid.⁵

Ovarian tumors span a wide spectrum. One large study of over 800 patients with ovarian tumors found that roughly one in six women with a malignant ovarian cancer also had a coexisting benign tumor or borderline lesion in the same ovary, and these coexisting conditions were more common in women under 55.⁶ Cervical cancer, driven largely by persistent human papillomavirus (HPV) infection, is another major category of pelvic malignancy, discussed further in the risk-factors section below.

Urological Tumors

Bladder cancer and prostate cancer are the two most common urological malignancies found in the pelvis. Prostate cancer in particular can grow locally to invade adjacent structures such as the seminal vesicles and bladder wall. Case reports describe advanced prostate tumors presenting as large pelvic masses visible on MRI, sometimes with bone metastases to the pelvis and femur.⁷ Because the prostate sits at the base of the bladder, advanced disease can blur the line between a “prostate tumor” and a “pelvic mass,” and multiparametric MRI is often needed to map precisely where the cancer has spread.⁸

Colorectal Tumors

Rectal cancer is the main colorectal malignancy that presents as a pelvic tumor. Even after successful initial treatment, rectal cancer can recur within the pelvis. These pelvic recurrences follow recognizable patterns: they can appear at the surgical connection site (anastomotic recurrence), grow anteriorly toward the bladder or reproductive organs, spread laterally toward the pelvic sidewall, or develop posteriorly against the sacrum. Lateral and posterior recurrences tend to have worse outcomes because they are harder to remove with clean margins and can invade nerves.⁹ Precise staging by a radiologist is critical for the surgical team because it determines the type of surgery needed and the likelihood that the entire tumor can be removed.¹⁰

Bone and Soft-Tissue Sarcomas

Sarcomas originating in the pelvic bones or the soft tissues surrounding them are rare but pose a distinct surgical challenge. The pelvis lacks the kind of natural tissue barriers found in the limbs, and vital nerves and blood vessels run close to the bone, making surgery complicated.¹¹ Pelvic soft-tissue sarcomas differ from their more commonly studied cousins in the retroperitoneum (the space behind the abdominal cavity). The most frequent subtype in the pelvis is leiomyosarcoma, whereas liposarcoma dominates in the retroperitoneum. Solitary fibrous tumors are also relatively common in the pelvis. Because pelvic sarcomas sit near the bladder and major vessels, surgery often involves managing vascular or urinary-system involvement.¹²

A multicenter Japanese study of 187 patients with pelvic and retroperitoneal bone or soft-tissue sarcomas found a three-year overall survival rate of about 72%. Larger tumor size at diagnosis was the most consistent predictor of worse outcomes across multiple measures, and osteosarcoma carried a poorer prognosis than other sarcoma types in this location.¹³

Symptoms That Can Signal a Pelvic Tumor

Pelvic tumors are frustrating diagnostically because their symptoms overlap with many everyday conditions. The specific symptoms depend on which structure the mass is pressing on or growing into, but some patterns are common:

• Pelvic pain or pressure: A dull ache or heaviness in the lower abdomen or pelvis is one of the most frequent complaints, especially with larger masses.
• Urinary changes: Difficulty urinating, increased frequency, or visible blood in the urine can result from a tumor pressing on or invading the bladder or ureters. In one case, a sacral chordoma compressed sacral nerves and caused urinary symptoms that initially looked like pelvic organ prolapse.¹⁴
• Bowel changes: Constipation, narrowing of stools, or rectal bleeding can occur when a mass compresses or invades the rectum or sigmoid colon.
• Abnormal vaginal bleeding: Bleeding between periods or after menopause is a classic warning sign for uterine and cervical tumors.
• Urinary obstruction: Large tumors can physically block a ureter, causing the kidney to swell. One case report documented a pelvic mass from pseudomyxoma peritonei compressing the right ureter and causing severe kidney swelling.¹⁵
• Leg pain or swelling: Tumors near the pelvic sidewall can compress veins or nerves, causing leg swelling or radiating pain down the leg.

Occasionally, a pelvic tumor announces itself through a more unusual symptom. One documented case involved a man with a pelvic sarcoma who developed severe episodes of low blood sugar, with glucose levels dropping below 40 mg/dL. The tumor was secreting a substance that mimicked insulin, a rare paraneoplastic phenomenon.¹⁶ Cases like this are uncommon, but they illustrate how pelvic tumors can produce symptoms that seem entirely unrelated to the pelvis.

Many pelvic tumors, particularly benign ones, produce no symptoms at all. They are found incidentally on imaging performed for another reason. Adnexal cysts (fluid-filled sacs on or near the ovary) are among the most frequent incidental findings on ultrasound, CT, and MRI, and most turn out to be harmless.³

Causes and Risk Factors

There is no single cause of pelvic tumors. The risk factors depend entirely on the type of tumor, but a few broad categories stand out.

Viral infection plays a major role in certain pelvic cancers. Persistent infection with high-risk strains of human papillomavirus (HPV), especially types 16 and 18, is considered a necessary cause of cervical cancer and anal squamous cell carcinoma.¹⁷ HPV works in part by triggering chronic inflammation in infected tissue, which promotes the accumulation of genetic damage over time.¹⁸ People living with HIV, men who have sex with men, smokers, and those with weakened immune systems face higher risk of HPV-driven pelvic cancers. The cervicovaginal microbiome may also play a role: disruption of the normal vaginal bacterial community appears to affect how well the body can clear HPV infection and may influence whether a persistent infection progresses toward cancer.¹⁹

Hereditary cancer syndromes account for a meaningful fraction of pelvic cancers. Lynch syndrome, caused by mutations in DNA-repair genes, raises the risk of colorectal cancer, endometrial cancer, and ovarian cancer. One case documented a woman with Lynch syndrome who developed both endometrial cancer and colon cancer simultaneously, both linked to a mutation in the MSH6 gene.²⁰ Beyond the well-known BRCA mutations associated with ovarian and breast cancer, researchers have identified other genes including BRIP1, RAD51D, and RAD51C that also carry elevated cancer risk, sometimes including pelvic cancers such as ovarian cancer.²¹

Other established risk factors include age (most pelvic cancers are more common in older adults), obesity (linked to endometrial cancer), chronic pelvic inflammation, and prior pelvic radiation therapy. For prostate and bladder cancers, smoking and occupational chemical exposures are well-documented contributors.

How Pelvic Tumors Are Diagnosed

Diagnosis usually starts with imaging and works toward a tissue sample. The specific tools depend on what the clinician suspects and where the mass appears to be located.

Ultrasound is often the first imaging step, especially for gynecological masses. It is inexpensive, widely available, and involves no radiation. Contrast-enhanced ultrasound has shown promise in distinguishing benign from malignant pelvic tumors, with one study reporting sensitivities above 90% for certain quantitative parameters.²² For deeper or more complex masses, MRI provides superior soft-tissue detail. In anal cancer staging, MRI identified a higher proportion of patients with advanced local disease compared with CT or PET/CT.²³ CT remains useful for evaluating the extent of disease spread beyond the pelvis and for planning radiation treatment, while PET/CT adds information about metabolic activity that helps detect metastases.

Structured MRI reports, where the radiologist fills in a standardized checklist of features rather than writing a freeform narrative, have been shown to improve the completeness of staging, particularly for features like involvement of the pelvic sidewall, depth of tumor spread, and vascular invasion.²⁴ This matters because surgeons rely heavily on imaging reports to plan operations, and incomplete reporting can lead to surprises in the operating room.

Blood-based biomarkers provide an additional diagnostic layer. CA-125 is the most widely used marker for ovarian masses, but it has a high false-positive rate in premenopausal women. Conditions like endometriosis can elevate CA-125 in more than half of cases. A newer marker called HE4 has shown better specificity: in a study of 391 women with benign pelvic masses, only about 2% had elevated HE4, compared with 37% who had a falsely elevated CA-125.²⁵ Another marker, CYFRA 21-1, has shown potential for stratifying ovarian cancer risk, though its use is not yet part of routine clinical practice.²⁶

Biopsy remains the gold standard for a definitive diagnosis. When a pelvic mass is accessible, ultrasound-guided aspiration through the vagina or rectum has proven safe and effective for obtaining tissue samples. In one retrospective study, all specimens obtained this way were adequate for diagnosis, and there were no post-biopsy complications.²⁷ For masses that are not accessible by these routes, CT-guided biopsy or surgical exploration may be necessary.

Conditions That Mimic Pelvic Tumors

One of the trickiest aspects of pelvic tumors is that several non-cancerous conditions can look almost identical to malignancy on imaging and even on clinical exam. Pelvic inflammatory disease, a common infection of the upper reproductive tract, is a well-documented mimic of ovarian cancer. In one cancer-center series, 41 out of 803 women who presented with suspicious pelvic masses turned out to have pelvic inflammatory disease after surgical exploration.²⁸ The researchers noted that when tumor markers are normal or only mildly elevated, especially in premenopausal women, pelvic inflammatory disease should be considered before committing to cancer surgery.

Xanthogranulomatous salpingo-oophoritis, a rare chronic inflammatory condition, is another notorious impersonator. It produces complex solid-and-cystic masses on imaging that closely resemble advanced ovarian cancer.²⁹ In postmenopausal women, an abscess arising within adenomyosis (a condition where the uterine lining grows into the muscle wall) can also raise strong suspicion of endometrial cancer.³⁰

These cases underscore why biopsy or tissue examination is so important before assuming a pelvic mass is cancer. Imaging alone cannot always tell the difference, and subjecting a patient to aggressive cancer treatment for a condition that needs antibiotics or minor surgery would be a serious error.

Pelvic Tumors in Children

Pelvic tumors in children are uncommon but not unheard of, and the types that occur are quite different from those seen in adults. Sacrococcygeal teratoma is the most prevalent congenital tumor in children and most often arises in the pelvic region, frequently diagnosed before birth on prenatal ultrasound. Ovarian teratoma, in its mature form, is the most common ovarian tumor in children and adolescents. Rhabdomyosarcoma, a cancer of developing muscle tissue, tends to appear in the bladder in both sexes and in the prostate in boys. Ewing sarcoma affects the flat bones of the pelvis and is another relatively common childhood pelvic malignancy.³¹

Diagnosing pelvic tumors in children follows similar principles to adults, with ultrasound and MRI playing central roles, but the treatment approach tends to be highly specialized. Pediatric oncology centers handle these cases because the growing body introduces surgical considerations that differ significantly from adult practice.

Pelvic Tumors Discovered During Pregnancy

A pelvic mass found during pregnancy creates a particularly difficult management decision. In one reported case, a retroperitoneal schwannoma (a benign nerve-sheath tumor) was initially mistaken for a large ovarian mass during pregnancy. The clinical team had to weigh three options: monitor the tumor and wait, operate during the pregnancy, or in extreme cases, consider ending the pregnancy.³² In that instance, the woman carried the pregnancy to full term and had the tumor removed after delivery. This approach is not always possible, particularly when the mass is malignant, rapidly growing, or causing obstruction, but it illustrates the preference for avoiding surgery during pregnancy when it is safe to wait.

Pregnancy-related hormonal changes can also cause existing benign tumors to grow faster or change in appearance on imaging, adding another layer of diagnostic complexity. Radiologists interpreting pelvic imaging in pregnant patients need to account for these normal physiological shifts to avoid overcalling benign findings as malignant.