Aberrations or Diseases of Lobular Development

Before the peri-menarchal period, the mammary gland consists of only a few ducts. During peri-menarchal development, the principal changes are duct sprouting and the addition of lobular structures. Estrogen induces connective tissue and vascular growth, which is required for new duct development. The lobules develop particularly during early reproductive life, between 15 and 25 years of age, and the different types have been described by Russo and coworkers. Each period of reproductive life (such as pregnancy, breastfeeding or menopause) is associated with increasingly more differentiated lobules. This explains the frequency of fibroadenoma during early reproductive life, which is an exaggerated development of various lobule structures.

Fibroadenomas are classified as benign, since they can almost be considered as aberrations of normal development.

Fibroadenoma Simplex: Aberration of Normal Development

The lobular origin explains many features of fibroadenoma, for instance its frequency during the menarchal period, which is a time of maximal lobular development. Fibroadenoma is the most common breast tumor of adolescence.

Indeed, its discovery is certainly less frequent by clinical examination than by ultrasound, which usually detects deeper fibroadenomas. The characteristics of adolescent fibroadenoma are accurate enough to be diagnosed certainly after only clinical examination. Often, the tumor is noticed accidentally by the adolescent herself. It is a firm, smooth, round or bosselated, painless and very mobile tumor. Its encapsulation explains this mobility.

The size of a fibroadenoma is generally from 1 to 3 cm. During the growth phase, the tumor doubles in size in 6 - 12 months and is then likely to remain static for the rest of the patient's life; it may even gradually decrease in size or disappear. In one study, Dent et al. followed 99 young women with clinical and cytological diagnoses of single or multiple fibroadenoma. They found that 107 lumps disappeared out of the 279 tumors followed over 7 to 9 years. In this work, the probability of fibroadenoma disappearance depended only on the young age of the patient. Fibroadenoma development is hormonedependent.

This dependence rapidly diminishes with the lesion's age and the appearance of fibrosis without hormonal receptors, a further possible explanation for the plateauing in the fibroadenoma's growth curve. Ultrasound confirms the evident clinical diagnosis. The ultrasonic features are round or oval sharp contour, weak internal echoes in a uniform distribution and intermediate attenuation, which is more evident if the tumor is young.

The histological features of fibroadenoma are an exaggeration of normal lobular development. The proliferation of stromal and epithelial elements is regular, maintaining a normal relationship as in a normal lobule. There is then a progressive sclerosis of the stromal element and the epithelial element disappears.