Metastatic prostate cancer with peritoneal carcinomatosis

A 73-year-old male with known history of prostate cancer with omental biopsy-proven malignant ascites presented for restaging study.

Patient underwent imaging with whole body PSMA PET-CT for restaging of metastatic prostate cancer with osseous metastases. Maximum intensity projection (MIP) PET demonstrated intense radiotracer activity along the peritoneum in the left abdomen (Figure 1). PSMA PET-CT revealed new increased radiotracer uptake along with peritoneum with soft tissue nodularity compatible with implants (Figure 2). Corresponding low-dose axial CT confirms implants and free fluid which correlates with malignant ascites (Figure 3). Coronal PET-CT shows hypermetabolic soft tissue nodularity along the peritoneum (Figure 4).

Prostate cancer metastasis most commonly presents as osteoblastic lesions in the axial skeleton. Other common sites of metastasis include distant lymph nodes, liver, and thorax. While it is exceptionally rare, a few cases of metastasis to the peritoneum have been described in literature [1].

When prostate cancer metastasizes to the peritoneum, it is often accompanied by additional metastasis and rarely as isolated metastases [2]. Prostate cancer is frequently advanced in the setting of peritoneal carcinomatosis and is associated with poor prognosis. Clinical presentation may include abdominal distention, pitting oedema of bilateral lower extremities, increased PSA levels and abnormal electrolytes [3]. Peritoneal involvement can be confirmed on imaging by the presence of peritoneal thickening or soft tissue nodularity on CT and radiotracer avid peritoneal implants on PSMA-PET. Peritoneal carcinomatosis is frequently associated with malignant ascites which may also demonstrate increased radiotracer uptake. Additional diagnostic studies include peritoneal biopsy and cytology [2].

Prostate cancer with peritoneal carcinomatosis is a rare presentation with limited published case studies. Late-stage prostate cancer with new onset ascites and elevated PSA following remission may be indications of peritoneal involvement [3]. Utilizing advanced imaging modalities for staging disease progression could lead to earlier detection of unique sites of metastasis. PSMA-PET is a newer imaging modality with high sensitivity for early detection and recurrence of prostate cancer. Increased use of PSMA-PET has led to detection of PSMA ligand uptake in non-prostatic diseases, raising a concern for false positives [5]. A recent prospective trial staging patients with recurrent prostate cancer identified a false positive rate of less than 10% [6]. Correlating PSMA-PET to CT and considering clinical context may reduce false positives. While PSMA-PET has revolutionized the management of prostate cancer, methods for increasing specificity should be explored along with its broader diagnostic potential.