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Q1: What is the differential diagnosis of a solid mass in a pregnant or lactating woman?
Breast masses are encountered frequently during pregnancy. As in non-pregnant women of childbearing age, most breast masses encountered during pregnancy and lactation are benign.1 The main differential considerations for a palpable solid breast mass in the pregnant or lactating female are listed in box 1. Of these, lactating adenoma and fibroadenoma are the two most prevalent. The incidence of breast cancer in this group of patients is low and the likelihood of diagnosing cancer in pregnancy or lactation is similar to that in the non-pregnant population.2 About 3% of breast cancers are diagnosed during pregnancy.1
Q2: What further work-up is needed to confirm the diagnosis in this case?
Due to the hypertrophic changes occurring in the breast during pregnancy and lactation, there is a dramatic increase in its radiographic density, which severely decreases the sensitivity of mammography for the diagnosis of breast masses. Ultrasound is the preferred initial study for evaluating a palpable mass in this group of patients. This determines the solid or cystic nature of the mass. However, once a solid mass is diagnosed, ultrasound cannot be relied upon to distinguish benign from malignant lesion and tissue sampling is usually warranted to avoid delay in diagnosis of breast cancer. Fine needle aspiration cytology has been associated with some false positive and false negative results, particularly in the setting of lactating adenomas.3 Ultrasound guided core biopsy is therefore often necessary for a definitive diagnosis.
Q3: What is the most likely diagnosis of this patient's palpable breast mass?
The breast mass in our patient is most likely a lactating adenoma as this is the most commonly encountered solid mass in a pregnant or lactating patient, accounting for as many as 70% of all biopsied lesions in this population.1 The clinical and sonographic features, although non-specific, are certainly compatible with this benign entity. Ultrasound guided core biopsy of the mass confirmed the diagnosis of lactating adenoma with some focal areas of necrosis.
Given the benign nature of the mass, a short term follow up was chosen. The patient continued to breast feed as usual. At follow up examination after three months, the mass was no longer palpable. A repeat ultrasound at this time confirmed complete resolution of the previously seen mass.
Main differential considerations for a palpable solid breast mass in the pregnant or lactating female
Lobular hyperplasia (normal physiological event in pregnancy).
Also called “lactational adenoma” or “breast tumour of pregnancy”, lactating adenoma is a benign stromal tumour that occurs only in association with gestation and is typically seen from the third trimester through the period of lactation. Clinically, it is generally a firm, mobile and non-tender mass, that usually regresses spontaneously after the cessation of breast feeding. Bromocriptine is occasionally used to induce shrinkage of these tumours.3Surgical excision of a persistent mass is generally deferred until the resolution of lactational changes. There is no convincing evidence for an association with use of oral contraceptives or an increased risk of breast cancer.4
The ultrasound features, although favouring a benign mass, are quite non-specific and may mimic malignancy. Characteristically, lactating adenoma is a solid mass between 1 and 4 cm in diameter, ovoid or macrolobulated, with well defined margins and its long axis parallel to the chest wall.3 It is typically homogeneous and hypoechoic with posterior acoustic enhancement. Hyperechoic fibrous bands coursing through the lesion and a prominent central duct have been described.3 Occasionally, however, indistinct or irregular margins, heterogeneous echotexture, and posterior acoustic shadowing may be present, making the distinction from a malignant mass more difficult.3 Core biopsy is often needed to confirm the diagnosis. Histopathologically, the mass lacks a true capsule and is composed of proliferating distended tubules and secretory lobules lined by uniform lobular cells with a granular and vacuolated cytoplasm, surrounded by a basement membrane and oedematous stroma.1 3 4 These gestational changes are characteristically out of phase with the actual stage of pregnancy. There maybe frequent mitotic figures, but there is no cellular atypia. Differentiation from lactational changes in a pre-existing fibroadenoma is possible since these changes in a fibroadenoma tend to be focal and the underlying characteristic architecture of the rest of the tumour is preserved.4 Lactating adenomas also have a distinctive immunohistochemical phenotype.4 Necrosis and haemorrhage are not prominent features of lactating adenomas, with only 5% demonstrating histological evidence of infarction.3Infarction may result in a rapidly enlarging mass that may reach considerable size.5
Lactating adenoma of the breast.