Background: The purpose of this study was to assess the role of prolactin (PRL) in men with locally advanced tongue cancer.
Methods: Circulating PRL was assayed immunoradiometrically in pretherapeutic and sequential blood samples of 99 patients with locally advanced tongue cancer. Patients were followed for 3 years or until their death within a stipulated time. Immunohistochemical localization of PRL was performed on formalin-fixed paraffin-embedded tissue sections. Tumoral prolactin receptors (PRLR) were estimated by ligand binding assay; the expression of PRL mRNA and PRLR mRNA were carried out by reverse transcriptase polymerase chain reaction (RT-PCR). Furthermore, PRL amplimer was sequenced and compared with human pituitary PRL amplimer.
Results: Pretherapeutic PRL levels were significantly higher in patients with locally advanced tongue cancer compared with controls (p =.01). Thirty-four percent (34 of 99) of the patients had hyperprolactinemia (PRL >/=15.0 ng/mL). Univariate survival analysis showed that patients with pretherapeutic hyperprolactinemia had a significantly shorter overall survival than patients with pretherapeutic PRL <15.0 ng/mL serum (p =.0009). In multivariate analysis, PRL emerged as the most significant independent prognostic factor influencing overall survival. Furthermore, changes in serial PRL levels showed excellent correlation with response to therapy and progression of disease. Forty-four percent (24 of 54) of the tumors showed positive immunoreactivity with PRL antibody, indicating that PRL or a molecule similar to it is produced by tongue tumors. PRL mRNA expression was seen in 85% (43 of 50) of the tumors and confirmed the de novo synthesis of PRL. Sequence analysis of the 234 bp PRL amplimer revealed that the sequence was homologous to exon 5 of pituitary PRL mRNA. The action of PRL is mediated by PRLR, and it was observed that the PRLR positivity by ligand binding assay was 33%. The expression of PRLR mRNA by RT-PCR showed two forms of PRLR mRNA (ie, intermediate form [500-600 bp] seen in 82% (41 of 50 ) of the tumors and the long form [800-900 bp] seen in 36% (18 of 50) of the tumors. In 82% (41 of 50) of the tumors, either the intermediate or long form was seen.
Conclusions: This multifaceted study of PRL suggests that tongue cancer cells produce PRL, and this ectopically produced PRL might be acting as a major local growth promoter by means of autocrine and paracrine mechanisms. Looking at its prognostic value and correlation with disease activity, it may provide new insights into treatment of tongue cancer.