Invasive micropapillary carcinoma of the breast and invasive breast carcinoma of no special type: a comparison of claudin proteins' expression and its impact on survival

Invasive micropapillary carcinoma of the breast is characterized by clusters of cells presenting with inverted polarity. Although the apico-basal polarity is a fundamental property of the epithelium, the biological alterations leading to the inside-out pattern observed in invasive micropapillary carcinoma (IMPC) remain mostly unknown. The regulation of tight junctions in polarity formation and maintenance is acknowledged. By using immunohistochemistry, we have analysed claudin-1, -3, -4, and -7 tight junction proteins expression and their prognostic value on IMPCs and compared them to invasive breast carcinomas of no special type (IBC-NST) tumors. Our cohort consisted of 37 IMPCs, 36 IBC-NST and 9 mixed IMPC/IBC-NST tumors. Two scoring systems were used to quantify protein expression: a 4-tier scoring system and the H-score method. Distant metastasis free survival (DMFS) intervals and overal survival (OS) data were used for prognosis evaluation. The analysed samples were characterized mainly by low or no claudin-1 expression whereas claudins-3, -4 and -7 showed variable positivity. We have found no significant differences in claudin-3 and -4 protein expression between IMPC and IBC-NST groups with either scoring methods, however high claudin-7 expression was found in significantly more IMPCs than IBC-NST tumors according to the H-score system (p = 0.02). The 4-tier scoring method revealed association of claudin-7 expression with molecular tumor subtypes (p = 0.001). IMPC and IBC-NST tumors did not show difference in DMFS (p = 0.70). In the analysis of pure IMPC and IBC-NST tumors, positive/high claudin-4 protein expression was significantly associated with shorter DMFS (p = 0.02/p = 0.008, respectively according to the two scoring methods). Claudin-3 and claudin-7 expression showed no association with DMFS or OS. Changes in epithelial polarity seem not to be related to claudin-1, -3, and -4 expression. Increased claudin-4 expression may have a role in breast cancer progression.