Protein-tyrosine kinases (PTKs) play important roles in regulating cell proliferation and differentiation during development. One member of the PTK family, PTK7, has been suggested to regulate the planar cell polarity (PCP) pathway in vertebrates and may play a role in neural convergent extension and neural tube closure. PTK7 has also been implicated in the development of cancer. Loss of PTK7 expression was seen in several melanoma cell lines and biopsies. Conversely, high-throughput analysis of acute myeloid leukemia samples showed an increased level of PTK7 expression compared to normal bone marrow and purified CD34+ cells. Multiple isoforms of PTK7 are known to exist.