The Role of P63 Immunocytochemistry for Myoepithelial Cells in the Diagnosis of Atypical and Suspicious Cases in Breast Fine Needle Aspiration Cytology (FNAC).

PURPOSE

Evaluation of the usefulness of p63 immunocytochemical marker for myoepithelial cells in the diagnosis of atypical and suspicious lesions in breast cytology.

PATIENTS AND METHODS

This is a retrospective study on 122 selected patients presented at Cytology Unit, Pathology Department, NCI, Cairo University, in three years interval from 2007 to 2009, with breast lumps who underwent preoperative FNAC and diagnosed cytologically as atypical or suspicious breast lesion for biopsy then they were followed by excisional biopsy for histopathologic assessment that was considered as the golden standard diagnosis against which FNAC diagnoses were compared. Paucicellular cytologic slides as well as cases with no corresponding final histopathological diagnosis were excluded. The destained cytologic slides were subjected to p63 immunocytochemical staining. Only the nuclear immunoreactivity for p63 was considered specific, cytoplasmic and membranous staining was considered nonspecific. The stained slides with p63 marker were quantified according to the percentages of positive epithelial cell clusters and positive single bare nuclei in the BACKGROUND. The immunocytochemical results were compared with histopathologic diagnoses.

RESULTS

Of the 122 studied breast aspirates, 84 cases with atypical findings and 38 cases with suspicious findings were included. The two categories yielded malignant diagnoses in 53 cases (63.1%) and 31 cases (81.6%), respectively. Invasive duct carcinoma was the most common malignant diagnosis in both categories. The most common benign diagnosis in the atypical group was fibrocystic changes (48.4%), while atypical ductal hyperplasia was the most common non-malignant diagnosis in the suspicious group (42.8%). P63 consistently stained the nuclei of myoepithelial cells, either overlying clusters and/or single bare nuclei. Of the histologically confirmed malignant cases 69% and 91.7% showed no p63 nuclear staining in cell clusters or bare nuclei, respectively; while cases showed staining pattern similar to that of benign lesions. On the other hand, 84.2% and 57.9% of the benign cases showed staining in more than 75% of the clusters and bare nuclei, respectively. The staining pattern of p63 was significantly different between malignant and benign lesions (p-value <0.005). The p63 sensitivity, specificity, positive, and negative predictive value were 90.5%, 84.2%, 92.7%, and 80%, respectively. Scattered p63 positive ductal cells ( <10% of duct cells) were detected in 6% of all malignant cases.

CONCLUSION

The p63 was a reliable nuclear marker of myoepithelial cells in breast cytology. Benign and malignant breast lesions showed significantly different staining pattern for p63 on inconclusive breast cytology. The diagnostic sensitivity, specificity, positive and negative predictive value of p63 marker were 90.5%, 84.2%, 92.7%, and 80% respectively. The p63 immunostaining may be used as a diagnostic adjunct to the routine fine needle aspiration cytology in cases of breast lesions with atypical and suspicious results.

KEY WORDS

P63 immunocytochemistry - Breast FNAC - Inconclusive diagnoses.