A 29 year old woman presents with a smoothly outlined spherical
mass on a screening mammogram. An FNA is performed. (Images 5A, 5B)
The FNA diagnosis is positive for malignant cells;
adenocarcinoma, favor lobular type. Due to the discrepancy between the FNA result and the clinical
impression (rule out fibroadenoma) a core biopsy is performed.
Figure 5A - This aspirate is a high cellularity with numerous single epithelial cells. A stromal fragment is apparent in this photomicrograph which might raise the possibility of a fibroadenoma, however, the marked cellularity and discohesion is worrisome. (Papanicolaou stain, low power)
Figure 5B - A higher power shows a monomorphic population of small bland nuclei in clusters and singly. The cells have feature of lobular neoplasia. This aspirate was from a fibroadenoma that was extensively involved by LCIS. (Papanicolaou stain, high power)
The false- negative rate is often the focus of discussion of breast FNA. Although overall sensitivity
and specificity rates in the literature for breast FNA are generally excellent, criticisms of breast FNA
generally revolve around false negative rate(FNR). Most series that have analyzed the FNR in breast FNA
have shown that the rate varies from 5 to 20% and is due predominantly to sampling errors by the
aspirator not to interpretative errors. The Triple Test or correlation of the mammographic, clinical and
cytologic findings is usually very helpful in these cases since a negative cytology and suspicious
mammographic lesion will be referred for core or open biopsy. Less attention is paid to the false
positive rate in breast FNA. The false positive rate is generally quite low, most series report a less
than 1% false positive rate. When we include false suspicious diagnosis, the rate is higher however in
this category an uncertainty regarding the diagnosis has been conveyed to the clinicians, therefore, most
patients will have further biopsy or frozen section confirmation prior to proceeding to definitive
surgical treatment. In the false suspicious/false positive category, many of the lesions are
fibroadenomas or fibrocystic changes with varying degrees of hyperplasia. Inflammatory lesions can also
be difficult to differentiate from malignancy and may elicit a false suspicious or positive diagnosis.
In this case presentation, I have presented the unusual circumstance of LCIS extensively involving a
fibroadenoma to make several points regarding breast FNA.
In the ideal world we would all practice cytology with all of the available clinical information. For
breast FNA it has clearly been demonstrated that incorporating the clinical and mammographic findings
improves accuracy and leads to improved patient management. At the time this FNA was interpreted the
information given was "rule out cancer", with no description of the mammographic or ultrasound
characteristics of the lesion. If the cytopathologist had known that this lesion was smoothly outlined
in a relatively young woman, a differential diagnosis could have been generated based on these findings.
The following chart gives a brief overview of breast neoplasms that present as smoothly outlined lesions
and their corresponding cytologic findings.
Smoothly Outlined Lesions of the Breast and their Cytologic Findings:
Cytologic Findings |
Staghorn epithelial clusters, stroma, naked (bipolar) nuclei |
Papillary Neoplasm ||
Papillary architecture, single cuboidal to columnar cells, little atypia |
Medullary Carcinoma ||
High grade malignant cells in sheets and single, background inflammatory cells |
Mucinous (Colloid) Carcinoma ||
Mucinous material in background with low grade cells in clusters and single, eccentric nuclei |
Histology and Clinical Follow-Up:
The core biopsy diagnosis is: Favor fibroadenoma involved by lobular carcinoma in situ. The lesion is excised and the
diagnosis is: Fibroadenoma with extensive involvement by LCIS.
Fibroadenomas, generally occur more commonly in young women, but can occur in any age group. The
other smoothly outlined lesion that occurs more frequently in younger women is medullary carcinoma. FNA
can be extremely useful in preventing delay in diagnosis in this circumstance as medullary carcinoma is a
straightforward cancer diagnosis on FNA. Mucinous carcinoma occurs more commonly in older woman and can
usually be diagnosed as malignant in FNA. Overlap does occur at times between papillary neoplasms and
fibroadenoma and mucinous cancers and fibroadenoma.
Typical Diagnoses In FNA Of Fibroadenoma
Simsir, et al reviewed 25 cases with a preoperative FNA diagnosis of FA with excision recommended due
to atypical features. In this series, 88% of FA with an atypical diagnosis were benign on excision.
There were two cases (8%) with a cancer diagnosis on biopsy. The false negative diagnoses were
attributed to sampling error and interpretative error. These authors recommended a conservative approach
to FNA which demonstrate a fibroadenomatous pattern but that have atypical features such as discohesion
and mild nuclear atypia.
Cancer Involving A Fibroadenoma
Rarely, carcinoma may involve a fibroadenoma. The most common type is lobular carcinoma in situ (more
than 50%) and 20% of the time ductal carcinoma in situ may be present in the FA. It has been shown that
if DCIS is confined to the FA it has less likelihood of recurring. LCIS is rarely diagnosed in breast
FNA as it is often an incidental finding in a biopsy for another reason. It is also difficult to
distinguish lobular from ductal cancer both invasive and in situ types in FNA. In general, classic
lobular carcinoma has monomorphic small uniform nuclei, bland chromatin and high nucelar/cytoplasmic
vacuoles. There may be intracytoplasmic vacuoles. These were the features seen in this case in addition
to marked cellularity so it is easy to see why a diagnosis of malignancy was made. The use of the triple
test saved this patient from unnecessary surgery. A core biopsy was done when the cytologic and
mammographic findings did not fit. The lesion was excised to rule out any invasive component.
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