Background: Basal cell carcinomas is one of the commonest cancer worldwide with a variable Nigerian prevalence of 7% to 20% of all histologically diagnosed cancers across Nigeria.

Basal cell carcinoma has various histologic subtypes which can be divided into low risk and high risk subtypes. The low risk subtypes include Superficial basal cell carcinoma, Nodular basal cell carcinoma (adenoid, cystic and keratotic variant, Pigmented basal cell carcinoma, Fibroepithelial basal cell carcinoma and Infundibulocystic basal cell carcinoma (BCC with adnexal differentiation). They have low risk of recurrence, less proliferation and low potential for malignancy. While the high risk include; uperficial micronodular basal cell carcinoma, Infiltrating basal cell carcinoma, Sclerosing/morphoeaform basal cell carcinoma, Basosquamous basal cell carcinoma and Basal cell carcinoma with sarcomatoid differentiation. having higher ability to metastasize, proliferate rapidly and have invasive tendencies.

Aims: This study analyzed the proliferative index using ki-67 immunoperoxidase protein of the histologic subtypes of basal cell carcinoma diagnosed in Federal Medical centre Umuahia, as to know the most dominant subtype of BCC and their proliferative index using Ki-67 in order to predict their biologic behaviors

Methodology: Archival FFPE blocks were retrieved alongside relevant clinical data. Hematoxylin and Eosin as well as immunohistochemistry using monoclonal antibody against Ki-67 (BioCare RM325C(RM)) stains were done on fresh 4-micron sections of tumour specimens to determine the antigen expression.

Result: The Ki-67 expression among the nodular variant of BCC, ranges from 1.2-15.2% with a mean value of 9.3%. The superficial variant expresses a Ki-67 expression value ranges from 2-18% with a mean value of 11.2%. The infiltrating variant of BCC has Ki-67 expression of a range of value from 14.4-28.2% with a mean value of 19.6%. Basosquamous variant has Ki-67 expression ranges from 21-45.6% with a mean value of 35.4%. The Sclerosing (morpheaform) variant has a Ki-67 expression ranging from 18- 32.7% with a mean value of 22.5%. The Proliferative index using Ki-67 nuclear stain of the low risk subtypes ranged from 1.2-18% with a mean value of 10%, while the high-risk subtypes have Proliferative index of 14.4-45.6% and a mean value of 25.1%.the most dominant variant is nodular BCC with the lowest proliferative index.

Conclusion: The high grade subtypes of cutaneous BCC, (infiltrating, Morpheaform and basosquamous BCC) possess a significant high proliferative index as high as 45.6% for basosquamous variant, a proliferative index that can be found in high grade carcinomas and sarcomas. Therefore, there is need for critical evaluation and follow up for all cases of BCC in order to isolate those with high proliferative index and manage accordingly.