Various molecular events of importance in tumour spread, like the gain and loss of adhesion molecules, secretion of proteolytic enzymes, increased cell proliferation, and the initiation of angiogenesis occur at the tumour-host interface (invasive front). We have hypothesised that molecular or morphological characteristics at the invasive front area of various carcinomas may reflect tumour prognosis better than other parts of the tumour. Consequently, we recently developed a simple malignancy grading system restricted to the deep invasive front area of head and neck squamous cell carcinomas. This grading system proved to have additional prognostic value over the established prognostic factors. All similar studies performed so far have confirmed the high prognostic significance of the invasive front grading in squamous cell carcinomas at different locations. In this review paper we describe the system and the hypothesis on which it has been developed. The reproducibility of the grading is acceptable for further extended studies. Interestingly, observations of similar invasive front alterations in different adenocarcinomas suggest that the invasive tumour front may underlie the biological aggressiveness of carcinomas of glandular origin, as well.