Background A new sensitive method for the detection of skin cancer micrometastases in lymph nodes is based on amplification of keratin 19 (K19) mRNA by reverse transcriptase–polymerase chain reaction (RT–PCR).
Objectives To compare results of RT–PCR with those of histological examination in terms of the detection rate of skin cancer micrometastases.
Methods Twenty-six lymph nodes obtained from 13 patients with squamous cell carcinoma (SCC), eccrine porocarcinoma and Paget's disease were investigated by histological examination (haematoxylin and eosin sections) and RT–PCR. RT–PCR was performed on extracted RNA by using K19 primer pairs. RT–PCR products were visualized by ethidium bromide staining and confirmed by non-radioactive hybridization with K19-specific probes.
Results All of 10 histologically positive lymph nodes yielded the expected 460-bp band. Of the 16 histologically negative lymph nodes, one (6%) was found by RT–PCR to express K19 mRNA, indicating the presence of micrometastases which could not be detected by histological examination. A serial dilution study using RNA extracted from SCC cells mixed with RNA extracted from normal lymph node cells showed a detection sensitivity of K19 RT–PCR of 10−5 µg cancer cell RNA in 1 µg lymph node RNA. Nested RT–PCR showed a detection sensitivity of one tumour cell in 106 lymphocytes.
Conclusions These results demonstrate the usefulness of K19 RT–PCR for the detection of skin cancer micrometastases in lymph nodes.