Phyllodes tumor is the most common primary breast malignancy in the adolescents. It is a stromal tumor arising from the lobular connective tissue [7]. A higher incidence has been reported in those with an Asian heritage. These tumors present as rapidly enlarging breast lumps. The benign types of phyllodes are more common in this age group. Phyllodes tumors occur predominantly in older women; however, about 5 % of these tumors are seen in girls younger than 20 years. Clinically, pathologically, and at imaging, these tumors may resemble a juvenile type of fibroadenoma [1]. Most tumors are larger than 6 cm with an average range of 8–10 cm [2]. A size less than 4 cm has a favorable prognosis as does presence of pushing rather than infiltrative borders, lack of necrosis, and lesser than three mitosis per high power field [1].

At sonography, these masses are circumscribed but tend to have a heterogeneous internal echotexture with clefts and cystic spaces compared to the more homogenous areas within a fibroadenoma (Fig. 11.3a, b). Mammography demonstrates a hyperdense circumscribed mass without calcifications; malignant types may exhibit pleomorphic microcalcifications. Recurrence is a feature noticed in both benign and malignant types; the former recurs about 10–25 % of the time and the recurrence rate in malignant phyllodes is greater than 40 % even following a wide excision [4]. About 5–24 % of phyllodes in those less than 20 years of age are malignant. Metastasis is uncommon but when present is hematogenous and to the lungs. Malignant types are histologically associated with sarcomatous elements, infiltrative margins, necrosis, cellular atypia, and increased stromal cellularity.

Breast carcinoma in girls under the age of 20 years is exceedingly rare, and based on the National Cancer Institute’s Surveillance Epidemiology and End Results data from 2006 to 2010, 0.0 % was diagnosed [16]. Less than 1 % of breast lesions in children is caused by breast cancer [17]. The most common type is the secretory carcinoma that presents as a circumscribed mass less than 3 cm and with a pseudo capsule [1, 11]. Prognosis is favorable. Breast cancer in these girls may be related to inherited BRCA1 and BRCA2 mutations [11]. Sonographic appearance is that of a malignant mass with irregular margins, taller than wide and with posterior acoustic shadowing.

The most prevalent malignant tumors in the breast in children and adolescents are metastasis. The most common tumors metastasizing to the breast are rhabdomyosarcoma, neuroblastoma, and hematolymphoid malignancies [1, 18]. Breast metastasis has been reported in 6 % of patients with rhabdomyosarcoma [18]. Metastasis are frequently bilateral and multiple although a solitary mass may also be seen. Clinically, masses may exhibit rapid growth and be painful. Sonographic appearance is variable and may exhibit a spectrum of appearance leading to an indeterminate morphology prompting a tissue diagnosis.

Nipple discharge in pregnancy is uncommon; cytological examination of spontaneous nipple discharge is performed. If no pathology is seen and physical and ultrasound examination is normal, clinical follow-up is advised. If pathologic results are seen on cytology, galactography may be indicated to exclude an intraductal lesion such as a papilloma. Nipple discharge is an uncommon manifestation of pregnancy-associated breast cancer [21].

Fibroadenomas being hormone-sensitive tumors may manifest varied appearances in pregnancy and lactation due to superimposition of hormone-induced and or lactational changes. Previously unsuspected fibroadenomas may be discovered in pregnancy due to enlargement and becoming palpable or symptomatic. Palpable fibroadenomas generally require tissue diagnosis that is best achieved with percutaneous core biopsy. Nonpalpable solid masses without suspicious morphology may be followed. The appearance of a fibroadenoma on ultrasound in pregnancy and lactation is varied and the following descriptions have been used [21]. Gravid fibroadenomas may demonstrate large cysts, dilated ducts, or increased vascularity (Fig. 11.4). Fibroadenoma with infarction may present as a painful tender mass. Intravascular thrombi have been identified on occasion in these fibroadenomas; this occurs usually in the third trimester. A more lobulated contour, heterogeneous architecture and posterior acoustic shadowing may be seen in such tumors as a result of infarction. Fibroadenoma with lactational changes and secretory hyperplasia demonstrates dilated ducts within, hyperechogenicity, and cystic changes. Aspiration may sometimes reveal milk as in a galactocele; distinction from a lactating adenoma may be difficult as well although this is not a management issue. Lactational adenoma histologically lacks the myoepithelial proliferation that is characteristic of fibroadenoma.

Galactoceles are the most common benign breast lesions in lactating women but are more frequently seen after cessation of lactation due to stagnation and retention of milk in the breast [21]. These are cysts that are lined with flat or cuboidal epithelium containing fluid that resembles milk that contains a variable amount of protein, fat, and lactose. The underlying etiopathogenesis is ductal dilatation, surrounding fibrous wall, and varying degrees of inflammation. Aspiration is diagnostic and therapeutic. The imaging appearance is variable depending on the contents:

Galactocele can have a complex cystic mass with thick internal septations. Aspiration causes the lesion to partially collapse and reveals milk-like aspirate (Figs. 11.7a–f and 11.8a, b).

Lactating adenomas are benign tumors of the breast typically seen in the third trimester and during lactation [20]. These masses resemble fibroadenoma clinically and on imaging appear as circumscribed mobile oval-shaped masses. When infracted, they appear as firm tender masses [22]. Histologically unlike a fibroadenoma, these have very little stromal elements and consist predominantly of epithelial elements. These elements consist of mature tubules containing actively secreting cells filling up the acini with secretions [22]. Lactating adenomas uniquely tend to regress after cessation of breastfeeding [23]. At sonography, posterior acoustic enhancement and increased lesion compressibility is characteristic likely due to large amount of secretions in the acini (Figs. 11.9a, b, 11.10a–c, and 11.11a–c) [22]. Infarction leads to appearance of irregular margins and posterior acoustic shadowing.

There is an increased frequency of benign proliferative disease during pregnancy and lactation [21]. Juvenile papillomatosis is generally seen in young women. An association with pregnancy has been proposed based on finding 5 cases of this entity in a series of 18 pregnant patients [21]. On ultrasound, juvenile papillomatosis appears as an ill-defined mass that is composed of multiple cysts surrounded by fibrous septa and well demarcated histologically from surrounding tissue. The cystic and ductal hyperplasia is associated with papillary hyperplasia lining the cystic spaces [24]. Definitive treatment is by surgical excision with negative margins required to avoid local recurrence [21]. In young women, juvenile papillomatosis is a risk factor for breast cancer with a reported association with breast cancer in 15 % of cases and a reported incidence of breast cancers in up to 50 % of female relatives [21, 24].

This is a rare benign tumor seen in young women. About 5–6 % are seen in the breast and more commonly seen in African American women. They arise from perineural cells. Clinically, these present as superficial firm masses and there may be associated skin changes [1]. Histologically, they tend to form an infiltrative growth and simulate an infiltrative carcinoma, clinically and on imaging. At sonography, these appear as 1–2 cm irregular masses with posterior acoustic shadowing and tend to exhibit characteristics of a malignant mass (Fig. 11.12a, b). At mammography, these may appear as spiculated masses and simulate invasive ductal cancers; these can also appear as well-circumscribed masses. Despite the malignant appearance on imaging, these tumors are benign and preoperative diagnosis is important to treat appropriately with wide excision [1].