Role of pre-operative FDG PET-CT scan in nodal and metastatic disease assessment in pelvic malignancies in treatment naive and post neoadjuvant chemotherapy setting.

Introduction: Pelvic malignancies predominantly include genitourinary or gynaecological and also colorectal malignancies, and staging these cancers accurately is crucial for management decisions and determining prognosis, especially lymph nodal staging. Accurate pre-operative staging is essential both in treatment naïve and in post neoadjuvant chemotherapy (NACT) setting in most pelvic malignancies. Both regional nodal and metastatic disease burden can usually be assessed on FDG PET-CT scan. Although FDG PET-CT is recommended for assessment of distant metastasis, PET-CT for regional nodal staging is still considered less sensitive, except in vulvar cancers where PET-CT is recommended now in NCCN guidelines even for nodal assessment. We would like to assess the role of FDG PET-CT scan in nodal and metastatic disease assessment in pelvic malignancies in pre-operative setting (treatment naïve and post chemotherapy).

Methods: 11 patients with different pelvic malignancies who underwent a pre-operative FDG PET-CT scan were studied retrospectively. These included, carcinoma urinary bladder (1), carcinoma endometrium (2), carcinoma rectum (2), carcinoma rectum post NACT (1) and carcinoma ovary post chemotherapy (5). Pre-operative FDG PET-CT scans were reviewed and nodal as well as metastatic disease burden was assessed. Lesions with abnormal increased FDG uptake more than background, and suspicious nodes >1cm with loss of fatty hilum were considered disease. These findings were then correlated with the post operative histopathological findings.

Results: Of the 11 patients, 5 were treatment naïve and 6 were post NACT and planned for surgery. Among the treatment naïve 5 cases, nodal metastasis were detected on FDG PET-CT scan in 3 patients with carcinoma urinary bladder (1), endometrium (1) and rectum (1), and node negative in the other 2 cases. These findings correlated excellently with post operative histopathological findings. Of the 6 cases post NACT, residual nodal disease on FDG PET-CT scan was detected in 2 cases of carcinoma ovary and 1 case of carcinoma rectum, and residual metastatic omental-peritoneal disease was detected in other 3 cases of carcinoma ovary with nodal metastasis in 1 of them. Almost all of these findings again correlated very well with the post operative histopathological findings, except nodal metastasis in the last case (<7mm and <1 mm foci).

Conclusions: Our study concludes that FDG PET-CT scan has a potential role in accurate nodal and metastatic disease assessment in preoperative assessment of pelvic malignancies in both treatment naïve and post neoadjuvant chemotherapy. However further larger studies would be required to determine diagnostic utility of FDG PET-CT scan in these cases.