On CT and MRI, the mass in the patient's colon looked like a malignant tumor. But when pathologists examined the tissue under a microscope, they did not find cancer.
Instead, they spotted Michaelis-Gutmann bodies, tiny layered mineral deposits that are the hallmark of malakoplakia, a rare inflammatory condition. The patient was treated with antibiotics, and two years later, follow-up imaging and endoscopy showed the mass had almost completely resolved.
The case was published Sept. 18 in BMJ Case Reports. It adds to a small body of reports showing how this obscure disease can impersonate colorectal cancer, and why a biopsy remains essential before major treatment decisions.
A Disease Born from Faulty Bacterial Cleanup
Malakoplakia is a chronic granulomatous disorder rooted in a malfunction of macrophages, the immune cells that swallow and digest bacteria. In people with the condition, macrophages take up bacteria but fail to fully break them down.
The leftover bacterial debris builds up and becomes mineralized with calcium and iron, forming Michaelis-Gutmann bodies. Proposed contributors include infection with bacteria, especially Escherichia coli, a weakened immune system, and faulty digestion inside immune cells. The disease was first described in 1902 by Michaelis and Gutmann, and its name, coined a year later, comes from Greek words meaning soft plaque.
The condition most often affects the urinary tract. The digestive system is the next most commonly involved area, and within it, the colon and rectum are frequent sites. Published tallies of colonic cases vary. The authors of a 2024 case report found 145 published case reports, while a 2025 report cited only a few dozen cases. Either way, the disease is rare.
Scans Can Suggest Cancer, but Only Tissue Can Confirm It
The latest report reflects a recurring diagnostic trap. Malakoplakia can form thickened, mass-like lesions that appear to invade nearby structures, a pattern radiologists associate with aggressive tumors.
Earlier cases show the stakes. A 2024 BMJ Case Reports article described a woman in her 70s, 13 years after a kidney transplant, whose CT showed a cecal mass highly suspicious for malignancy. The mass was surgically removed, and it turned out to be malakoplakia, which was treated with surgery plus a prolonged course of antibiotics.
In a 2021 case in the Journal of Surgical Case Reports, a 75-year-old man's CT showed thickening of the descending colon that appeared to involve his left kidney, a hip flexor muscle, and the tissue behind the abdomen. Suspecting advanced cancer, surgeons removed part of his colon, part of a kidney, and surrounding tissue. Pathology revealed malakoplakia, and his symptoms resolved during follow-up.
The disease does not always form a large mass. A 2026 report from Japan described a patient on hemodialysis and steroid therapy whose screening colonoscopy found two reddish polyps that resembled precancerous growths. Only after the polyps were removed did the microscope reveal malakoplakia.
In the new case, tissue analysis identified the disease before definitive cancer treatment, allowing doctors to pursue antibiotics instead. The near-complete disappearance of the mass over two years, seen on both imaging and endoscopy, supports the benign diagnosis.
Who Tends to Develop Malakoplakia
Most patients have weakened immune systems. An August 2026 case series from Western University in Ontario, published in the journal Diseases, described four patients whose malakoplakia developed after liver transplantation, after kidney transplantation, during relapsed acute myeloid leukemia, and during immunosuppressive treatment for ulcerative colitis. Their presentations ranged from incidental findings on endoscopy and tumor-like colon masses to recurrent bloodstream infections and kidney transplant dysfunction. Management ranged from antimicrobial therapy and observation to surgery when needed.
The researchers noted that malakoplakia can mimic infectious, inflammatory or cancerous conditions, creating significant diagnostic challenges.
Healthy people are not entirely exempt. A 2025 BMJ Case Reports article from Henry Ford Health described colonic malakoplakia in an otherwise healthy woman who had no symptoms and was undergoing a screening colonoscopy. The authors noted that treatment guidance remains limited and, citing the condition's potential for serious illness and death, urged thorough evaluation even in patients without symptoms.
Symptoms, when present, can include abdominal pain, diarrhea, and rectal bleeding. None of these is specific to malakoplakia.
Antibiotics Instead of the Operating Room
Because the disorder involves bacteria that immune cells fail to clear, treatment often centers on antibiotics. Fluoroquinolones such as ciprofloxacin are frequently used because they build up inside macrophages, where the bacteria persist. Some reports have also described agents meant to boost macrophage killing ability, such as bethanechol and vitamin C, though evidence for them is limited.
Surgery still has a role for large masses or complications such as bowel obstruction. When medically possible, reducing immune-suppressing drugs may also be considered for transplant recipients and others who take them.
The case does not change how doctors evaluate suspected colon cancer, which is far more common than malakoplakia. Instead, it reinforces a basic rule of cancer care: suspicious imaging raises the question, and tissue diagnosis answers it.
Key Questions Answered
What is colonic malakoplakia?
It is a rare, benign chronic inflammatory disease in which immune cells fail to fully destroy bacteria, which can lead to mass-like lesions in the colon.
Why did the mass look like cancer?
Malakoplakia can form thick, invasive-looking lesions on CT and MRI that resemble malignant tumors.
How was the correct diagnosis made?
Examination of tissue under the microscope revealed Michaelis-Gutmann bodies, which are characteristic of malakoplakia.
How is malakoplakia treated?
Antibiotics that penetrate immune cells, such as fluoroquinolones, are commonly used. Surgery may be needed for large masses or complications.
Does this mean a suspicious colon mass is likely benign?
No. Colorectal cancer is far more common. The case shows why biopsy confirmation is needed before treatment.
