• adenoid cystic carcinoma;
  • breast carcinoma;
  • collagenous spherulosis;
  • papillary growth pattern

Adenoid cystic carcinoma (ACC) is rare in breast carcinomas and has a relatively better prognosis than other histological types. Although the tumor shows various growth patterns, such as those of salivary glands or other organs, the papillary growth pattern is uncommon. Collagenous spherulosis (CS), consisting of intraluminal clusters of eosinophilic spherules situated adjacent to, or encompassed by, usually benign proliferative epithelium, is also a rare incidental microscopic finding that ACC must be distinguished from, and it has never been reported in association with ACC. We present a case of ACC arising in mammary ducts with the papillary growth pattern and CS-like structures that should not be mistaken for benign proliferative lesions, especially in the core needle-biopsy specimen, because the adenoid cystic pattern might not always be contained in the specimen. Morphologically and histochemically, the results suggest that the CS-like structures in the present case undergo a similar process to the originally described CS, which the myoepithelium is thought to be associated with. Examination of more cases are necessary to clarify the process of CS and its relationship to mammary proliferative lesions.