Characterising Metastatic Penile Cancer Using Molecular Imaging - Hybrid MRI-PET [MRI-PET]

Overview

The presence of metastatic disease in the lymph nodes within the groin is the most important factor in predicting the long-term outcome for patients diagnosed with penile cancer. In the majority of patients diagnosed with penile cancer obvious abnormalities cannot be felt in the groin even though the cancer may have already spread to the lymph nodes in the groin. In these patients, a procedure called Dynamic Sentinel Lymph Node Biopsy (DSLB) is required to determine if the cancer has spread to the lymph nodes in the groin. In DSLB a radioactive substance is injected at the site of the penile cancer and then travels to the lymph nodes in the groin which are then biopsied. This procedure requires a general anaesthetic and an in-patient hospital stay. In approximately 20% of patients with penile cancer obvious abnormalities can be felt in the lymph nodes in the groin. However, any abnormality detected may not necessarily be due to metastatic disease. In order to confirm if metastatic disease is present in the lymph nodes of these patients a biopsy is also required. However in these patients the lymph nodes are detected and biopsied using an ultrasound scan rather than by passing a radioactive substance into the body. MRI-PET is a new procedure which combines conventional MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography) scans into one scan. MRI - PET scans create very clear pictures of internal body structures. MRI-PET is a non-invasive procedure which can be performed on an out-patient basis. The accuracy of MRI-PET in detecting metastatic penile cancer is not known. The main purpose of this study is to establish the effectiveness of MRI-PET compared to DSLB and ultrasound guided biopsy in detecting the presence of metastatic disease in the lymph nodes of patients with penile cancer. If effective, MRI-PET could replace the invasive procedures currently required for detection of metastatic penile cancer.

Penile cancer is a neglected area in terms of clinical and molecular research due to the relatively low incidence of the disease (age standardized incidence is 0.3 - 1 per 100,000 men in European countries and the USA). Inguinal nodes are impalpable in up to 80% of penile cancer patients on presentation. However, 20% of these will harbour occult metastases. Therefore radical inguinal lymphadenectomy, with its significant associated morbidity of up to 70% (and mortality), is an unnecessary surgical procedure in the majority of patients. There are presently only limited data available from small series pertaining to the role of radiological imaging modalities establishing the presence of lymph node metastases, particularly micrometastases, in patients with squamous cell carcinoma of the penis. Thus there is no clear role at the moment for radiological investigations in staging men with impalpable inguinal lymph nodes at presentation. Dynamic sentinel lymph node biopsy is an invasive procedure which utilizes lymphoscintigraphy but still requires surgical excision of the lymph nodes. Simultaneous PET and MRI using new hybrid MRI-PET systems promises optimal spatial and temporal co-registration of structural, functional, and molecular image data. The theoretical advantages of hybrid MRI-PET scanning compared to CT-PET are better soft tissue resolution, which is advantageous for the small lymph nodes, and also decreased radiation exposure. Also, local staging of the primary penile tumour could be performed simultaneously with the inguinal lymph nodes using MRI-PET. If effective, MRI-PET would provide a single non-invasive imaging test that would replace dynamic sentinel lymph node biopsy (which is operator dependent, involves a general anaesthetic, in-patient hospital stay and has associated morbidity) in the detection of micrometastatic deposits in those patients with cN0 (impalpable inguinal lymph nodes) disease. In addition to this, a single MRI-PET sequence will also stage the primary lesion. University College London Hospital (UCLH) manages the largest number of penile cancer patients in the United Kingdom (UK). Hybrid MRI-PET is a new imaging modality which could result in significant cost savings, and more importantly, avoid invasive operative procedures necessitating in-patient hospital stay (with the associated potential for significant morbidity). UCLH currently has the only hybrid MRI-PET scanner in the UK. This research is unique and groundbreaking and could have a dramatic impact for penile cancer patients. Additionally, as serum, blood and frozen tissue from this cohort of patients will be collected and stored , this will provide an extremely valuable resource for future translational studies.