Histological evaluation of the possible transformation of peripheral giant cell granuloma and peripheral ossifying fibroma: A preliminary study.

Aims: The objective of this study is to describe shared morphological features of peripheral giant cell granuloma (PGCG) and peripheral ossifying fibroma (POF) in detail and discuss the possible relationship between them.
Materials and Methods: Ten intermediate cases with features resembling to both POF and PGCG were selected and type 3 and 1 collagen immunostainings were performed for evaluation of the connective tissue maturation. Immunohistochemical staining percentage (SP) for stromal cells in the slides of POF and PGCG counterparts of intermediate lesions was scored as 1 when the SP was above 10%, 2 when the SP was above 25%, 3 when the SP was above 50% and 4 when the SP was above 75%. Staining intensity (SI) of immunuhistochemical staining was graded and scored as 1 - mild, 2 - moderate, and 3 - severe. An immunoreactivity score was calculated by multiplying SP and SI.
Results: All intermediate lesions comprised osteoclast type multinucleated giant cells and partly mineralized hard tissue component. Parts of intermediate lesions resembling POF showed higher type 1 collagen immunoreactivity compared to the PGCG counterparts of intermediate lesions (P < 0.05). PGCG counterparts showed higher type 3 collagen immunoreactivity compared to the POF counterparts of the intermediate lesions (P < 0.05).
Conclusion: POF may be a later stage lesion with morphologically more mature components. A possible transformation may be considered for these two lesions.