Immunohistochemical analysis of negative inguinal lymph nodes in men with squamous cell carcinoma of the penis: are we missing micrometastases which could predict recurrence?

OBJECTIVE: To determine the presence or absence of micrometastases in lymph node dissection specimens of men with squamous cell carcinoma (SCC) of the penis using immunohistochemistry, and to correlate the results with clinical outcome.

PATIENTS AND METHODS: In all, 13 men (mean age 55.8 years) with penile SCC, treated at St George's hospital between 2001 and 2005, were selected. All had prophylactic lymph node dissections; (12 bilateral and one unilateral). All lymph nodes were negative on standard haematoxylin and eosin (H&E) staining. Each block was stained for cytokeratins MNF 116 and LP34. In all, 217 lymph nodes were examined (mean 16.7 per patient). The median (range) follow-up was 23 (10-52) months.

RESULTS: The mean tumour size and depth of invasion were 30.2 mm and 15.9 mm, respectively. There were eight T2 and four T3 tumours. Four tumours showed lymphovascular invasion. Information on tumour size and pathological grade was not available in one case. None of the patients have to date developed a local recurrence. A single lymph node was found to contain a micrometastasis, which was identified retrospectively on the original H&E slide. This measured 0.24 mm in maximum dimension. This patient had a T2G2 tumour with no vascular invasion; he has not progressed clinically in 10 months of follow-up.

CONCLUSIONS: Anticytokeratin immunohistochemistry on H&E-negative inguinal dissection specimens in men with SCC of the penis can detect micrometastases that might be overlooked on routine stains. Their prognostic and therapeutic significance needs further study.