Rare Prostate Cancer Associated with Cushing’s Syndrome in Case Report

A patient with depression developed Cushing’s syndrome (CS) because of a rare ACTH-secreting small cell cancer of the prostate, a case study reports.

The case report, “An unusual cause of depression in an older man: Cushing’s syndrome resulting from metastatic small cell cancer of the prostate,” was published in the “Lesson of the Month” section of Clinical Medicine.

Ectopic CS is a condition caused by an adrenocorticotropic hormone (ACTH)-secreting tumor outside the pituitary or adrenal glands. The excess ACTH then acts on the adrenal glands, causing them to produce too much cortisol.

Small cell cancer is more common in older men, those in their 60s or 70s. Sources of ectopic ACTH synthesis arising in the pelvis are rare; nonetheless, ACTH overproduction has been linked to tumors in the gonads and genitourinary organs, including the prostate.

Still, evidence suggests there are less than 30 published cases reporting ectopic CS caused by prostate cancer.

Researchers from the Southern Adelaide Local Health Network and the Royal Adelaide Hospital in Australia described the case of an 84-year-old man who complained of fatigue, back pain, and lack of appetite.

Blood tests revealed mildly elevated prostate-specific antigen (PSA) and creatinine levels, which could indicate the presence of prostate cancer and impaired kidney function, respectively.

The patient had a history of locally invasive prostate cancer even though he didn’t experience any symptoms of this disease.

Ultrasound examination showed an enlarged prostate plus obstructed ureters — the tubes that carry urine from the kidney to the bladder. To remove the obstruction, doctors inserted a thin tube into both ureters and restored urine flow.

After the procedure, the man had low levels of calcium, a depressed mood, and back pain, all of which compromised his recovery. Imaging of his back showed no obvious reason for his complaints, and he was discharged.

Eight days later, the patient went to the emergency room of a large public hospital because of back pain radiating to his left buttock. The man also had mild proximal weakness on both sides. He was thinner, and had low levels of calcium, high blood pressure and serum bicarbonate levels, plus elevated blood sugar. In addition, his depression was much worse.

A psychiatrist prescribed him an antidepressant called mirtazapine, and regular follow-up showed that his mood did improve with therapy.

A computed tomography (CT) scan revealed a 10.5 cm tumor on the prostate and metastasis on the lungs and liver. Further testing showed high serum cortisol and ACTH levels, consistent with a diagnosis of Cushing’s syndrome.

But researchers could not identify the ACTH source, and three weeks later, the patient died of a generalized bacterial infection, despite treatment with broad-spectrum antibiotics.

An autopsy revealed that the cancer had spread to the pelvic sidewalls and to one of the adrenal glands. Tissue analysis revealed that the patient had two types of cancer: acinar adenocarcinoma and small cell neuroendocrine carcinoma — which could explain the excess ACTH.

Cause of death was bronchopneumonia, a severe inflammation of the lungs, triggered by an invasive fungal infection.

Investigators believe there are things to be learned from this case, saying, “Neither the visceral metastases nor aggressive growth of the pelvic mass noted on imaging were typical of prostatic adenocarcinoma. [Plus], an incomplete diagnosis at death was the precipitant for a post-mortem examination. The autopsy findings were beneficial to the patient’s family and treating team. The case was discussed at a regular teaching meeting at a large tertiary hospital and, thus, was beneficial to a wide medical audience.”

Although a rare cause of ectopic ACTH synthesis, small cell prostate cancer should be considered in men presenting with Cushing’s syndrome, especially in those with a “mystery” source of ACTH overproduction.

“This case highlights the importance of multidisciplinary evaluation of clinical cases both [before and after death], and is a fine example of how autopsy findings can be used to benefit a wide audience,” the researchers concluded.