Perianal Metastasis from Lung Adenocarcinoma Presenting as an Acute Abscess: A Case Report and review of the literature
This case report describes an exceptionally rare instance of a 76-year-old man with lung adenocarcinoma presenting as a perianal abscess, highlighting the critical need for early histopathological evaluation of atypical perianal lesions to avoid unnecessary surgery and enable timely systemic treatment.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Most people understand that when cancer spreads from one part of the body to another, it usually heads toward the liver, the bones, or the brain. These are the well-worn paths of the disease, predictable enough that doctors know to check them first. But cancer is a master of disguise, and sometimes it takes a route so unexpected that it tricks even experienced physicians. This is the story of a rare and dangerous trick played by lung cancer, a disease that typically begins in the lungs but can occasionally hide in the most unlikely places, such as the skin and tissue around the anus. When this happens, the cancer does not look like a tumor; it looks like a common, painful infection. The danger lies in this deception: if a doctor treats it as a simple infection, the underlying cancer goes unnoticed, and the patient loses precious time.
The case that brings this danger into focus involves a seventy-six-year-old man who arrived at a hospital in Wuhan, China, in October 2025. He had spent fifty years smoking, a habit that had left him with a history of lung nodules and breathing difficulties. For three months, he had been coughing up white mucus, and for the last month, he had been in pain near his anus. When he was examined, the area around his anus was red, swollen, and tender to the touch. It felt exactly like an abscess, a pocket of pus caused by a bacterial infection. The standard treatment for such a condition is a minor surgery to cut it open and drain the fluid. The medical team proceeded with this plan, expecting to find a simple infection.
Inside the operating room, however, the picture changed. As the surgeons made the incision, they did not find just a bag of pus. They found a hard, solid lump of tissue that was about the size of a small plum. While they drained a small amount of fluid, the presence of this solid mass was a warning sign that something was wrong. The tissue was sent to a laboratory for a closer look under a microscope. The results were a shock. The cells were not bacteria or simple inflammatory tissue; they were cancer cells. Specifically, they were a type of lung cancer called adenocarcinoma that had traveled all the way from the lungs to the anal region. The cells had even changed their appearance, taking on a rough, aggressive look known as sarcomatoid differentiation, which often signals a very fast-growing and difficult-to-treat disease.
To confirm where this cancer had come from, the team performed a bronchoscopy, a procedure where a thin tube is passed down the throat to look inside the lungs. They found a tumor in the lower part of the right lung, confirming that the lung was the original source. The cancer had spread through the body and settled in the anal area, mimicking a harmless infection so perfectly that it nearly fooled the doctors. The patient's condition deteriorated quickly. Despite receiving strong antibiotics to fight the infection, his lungs continued to fill with fluid and inflammation. He passed away from respiratory failure just one week after the initial surgery. The family chose comfort care, and no further cancer treatments were attempted because the patient was too weak.
This tragic outcome highlights a critical lesson for the medical world. The paper documents that while lung cancer spreading to the anal area is incredibly rare—only about twenty such cases have ever been recorded in medical literature—it is a real possibility. The study emphasizes that when a patient with a history of cancer, or a heavy smoking history, develops a lump or sore in the anal region that looks like an abscess, doctors must be extremely careful. They cannot assume it is just an infection. If a surgeon cuts into a lump and finds solid tissue mixed with pus, that tissue must be tested immediately. The presence of infection does not rule out cancer; the two can exist together.
The researchers reviewed other similar cases from history to understand the pattern. They found that most of these rare metastases occur in patients with non-small cell lung cancer, the most common type of the disease. In many of the past cases, the cancer was mistaken for a benign condition, leading to delays in treatment. This specific case was unique because the cancer appeared as an acute abscess, a presentation that is even rarer than a simple lump or ulcer. The study concludes that the key to survival in these rare instances is a high level of suspicion. Doctors must remember that a hard mass found during a procedure for a supposed infection is a red flag. By testing that tissue early, they can identify the cancer before it is too late, allowing for the correct systemic treatment rather than just treating the symptoms. In this case, the diagnosis came too late to save the patient, but the report serves as a vital reminder to the medical community to look deeper when the signs seem too simple to be true.
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