This early phase I trial studies how well ultrasound-guided photoacoustic imaging works in telling the difference between healthy and cancerous inguinal (groin) lymph nodes and how well it can detect certain features of lymph nodes, including size and shape in patients with cancer. Ultrasound-guided photoacoustic is a non-invasive imaging method that can detect and display characteristics of lymph nodes based on the level of oxygen in the cells. This imaging method may provide more accurate tumor staging and prevent unnecessary surgical interventions.

PRIMARY OBJECTIVE:

I. To estimate the mean difference in oxygen saturation (%sO2) between healthy and malignant inguinal lymph nodes using ultrasound-guided photoacoustic imaging (PAI) in cancer patients.

SECONDARY OBJECTIVE:

I. To examine the role of ultrasound-guided PAI in detecting metastases in the inguinal lymph nodes and ultrasound features of lymph nodes such as the size, shape of the lymph nodes.

OUTLINE:

Patients undergo standard of care ultrasound of the lymph nodes, then undergo ultrasound-guided PAI over 3-5 minutes. Patients then undergo standard of care ultrasound-guided fine needle aspiration (FNA) or biopsy a suspicious lymph node.

After completion of study, patients are followed up for 3 months.

Inclusion Criteria:

• Pathologically proven primary malignancy
• Suspicious inguinal lymph nodes for metastasis on a conventional imaging modality
• Scheduled to undergo ultrasound-guided fine needle aspiration cytology or biopsy

Exclusion Criteria:

• Melanoma patients, since the melanocytes may have a "masking effect"
• The deeper inguinal lymph nodes (3-5 cm deep) and smaller (< 1 cm in short axis) in dimensions will be excluded from the study