[476] Expression of Ki-67 in Benign, Atypical, and Malignant Hidradenomas

RM Nazarian, P Kapur, A Piris, MC Mihm, MP Hoang. Massachusetts General Hospital, Boston, MA; UT Southwestern Medical Center, Dallas, TX

Background: The histologic features of an atypical hidradenoma are worrisome for an increased risk of recurrence and possible malignant potential; however, prior studies with immunohistochemistry or follow-up have not been reported. In addition, immunohistochemical analysis of hidradenocarcinoma exists in the literature mainly as case reports and a single series of six cases.
Design: Archival materials were retrieved from the MGH pathology (1978-2008) and MCM consultation files (2000-2006). The slides were reviewed by MPH and MCM and the following features were graded as either present or absent: loss of circumscription, infiltrative growth pattern, deep extension, necrosis, perineural invasion, vascular invasion, nuclear pleomorphism, and greater than 4 mitoses per 10 high-power fields. Tumors with > 3, 1 or 2, and none of the cited features were classified as malignant, atypical, and benign hidradenoma, respectively. Eight metastasizing adnexal carcinomas were included as the control group. Percentage of Ki-67 immunoreactivity was scored and averaged for 5 HPFs (500 cells per field) independently by RMN and MPH. The mean Ki-67 scores of the different groups were compared using Mann-Whitney U non-parametric tests.
Results: A statistically significant difference (two-tailed p value of < 0.05) in mean Ki-67 expression was observed between group #1 vs #2 (p=0.045), #1 vs #3 (<0.001), #1 vs #4 (0.002), #2 vs #3 (<0.001), #2 vs #4 (0.002) (see table 1). Follow-up was available for 6 hidradenocarcinomas (range: 2 months to 2 years; median: 11 months) and showed no evidence of disease. Follow-up was available for 11 atypical hidradenomas (range: 6 months to 16 years; median: 2 years) and showed no recurrences.

Ki-67 (%)	(#1) Benign hidradenoma	(#2) Atypical hidradenoma	(#3) Malignant hidradenoma	(#4) Metastasizing adnexal carcinoma
N	7	15	11	8
Median (range)	1.93 (0-6.8)	4.65 (2.36-11.45)	33.06 (13.95-47)	26.0 (7.15-40.8)
Mean	3.06	6.23	30.39	24.42

Conclusions: Our findings show that atypical hidradenoma has a significantly lower Ki-67 expression compared to the malignant counterpart and the metastasizing adnexal carcinoma, and only approaches statistical significance (p=0.045) compared to the benign hidradenoma group. The results suggest that these tumors are likely to recur but unlikely to metastasize. Ki-67 may be a helpful diagnostic adjunct in classifying hidradenoma in the setting of small biopsy specimen.
Category: Dermatopathology

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 68, Tuesday Afternoon