Breast cancer is divided into several clinical subtypes that includ ductal carcinoma in-situ (DCIS), infiltrating ductal carcinoma (IDC), lobular carcinoma in-situ (LCIS), infiltrating lobular carcinoma (LC), as well as into different stages from 0 to IV (based on tumor size and metastatic propensity). BRK (also pronounced “berk”) is a prototypical member of a family of non-receptor tyrosine kinases previously referred to as the FRK/PTK6 or PTK6 family kinases. The mammalian BFKs comprise three members namely, BRK or protein tyrosine kinase 6 (PTK6), FRK(PTK5) and SRMS (src-related kinase lacking C-terminal regulatory tyrosine and N-terminal myristylation sites or PTK70). 
Like their Src family counterparts, members of the BRK family kinases are composed of the classic Src homology 3 (SH3), the Src homology 2 (SH2) and the kinase (SH1) domains. However, unlike Src family kinases (SFKs), the BFKs typically lack membrane-anchoring N-terminal myristoylation and palmitoylation signals, thereby rendering them soluble and potentially widening their accessibility to intracellular substrates. The BFKs are also evolutionarily distinct from SFKs by their unique exon organization. All three mammalian BFK members possess 8 exons interspersed between 7 introns in a conserved/identical manner. Src42a/Dsrc41, a tyrosine kinase belonging to the Drosophila melanogaster species, is the only other off-species relative known to exhibit significant intron-exon splice pattern similarity with the BFKs.

References

1.Goel RK, et al. Biochim Biophys Acta. 2015;1856(1):39–54.