Primary breast mucosa-associated lymphoid tissue (MALT) lymphomas are uncommon and restricted diagnostic criteria should be used to exclude breast involvement by systemic lymphomas. The molecular pathogenesis of primary breast MALT lymphomas is not clear because of the rarity of the disease. Generally the molecular studies of MALT lymphoma in extranodal sites have shown the presence of different chromosomal aberrations, mutually exclusive with substantial differences in their frequency relatively to topographic localization. Few cases of breast MALT lymphomas in the literature have been assessed for MALT lymphoma-associated translocations and BCL10 expression, underlying their rarity in primary breast MALT lymphomas. In our study, we analyzed a series of nine cases of primary breast MALT lymphomas. FISH results showed evidence of MALT1 gene rearrangements in four primary breast lymphomas, in particular three cases with t(11;18)(q21;q21) and one case with t(14;18)(q32;q21). In addition, BCL10 gene rearrangement was not observed. There was no evidence of BCL10 gene translocation in any of the neoplasms assessed. Our data indicate that MALT1 gene rearrangements are not rare in primary breast MALT lymphoma in contrast with results of previous series. Finally, t(11;18) has been observed to be significantly associated with high intensity cytoplasmic BCL10 expression underlying cross-talk between MALT1 and BCL10 pathways in the pathogenesis of MALT lymphomas.