anon asking rcb means since these capital letters were in a repeated tweet

mirror it–

BCR - breakpoint cluster region (in genes)

BCR gene is the site of breakpoints used in the generation of the 2 alternative forms of the Philadelphia chromosome translocation found in chronic myeloid leukemia (CML; 608232) and acute lymphocytic leukemia (Groffen et al., 1984; Shtivelman et al., 1985; Hermans et al., 1987).

BCR - baseline change request

BCR - battlefield communications review

BCR - Benefits Cost Ratio

BCR - Bureau Collection Recovery

BCR - B cell receptor (medical)