Working in a histology lab means that I get to see a lot of what our body looks like under the microscope. Quarterly I will share with you some of my photos from the microscopic world of our inner space and tell you a little bit about what we’re looking at.
This quarter we’re taking a look at a very common benign tumour of the breast; a fibroadenoma.
There are huge clues in the name that describe the composition of this tumour; the word “fibro” suggests a composition of fibres (usually connective tissue), and “adeno” is derived from a word meaning “glandular”. By throwing an “-oma” at the end, that just basically tells us that it is a tumour of some sort.
Fibroadenomas (or “FADs”, as we call them in the lab), generally present as a firm, often mobile lump, and typically in women aged in their 20s or 30s.
They are benign lesions. There is so little worry about them developing into something more sinister, that once one is unequivocally confirmed on a breast scan, not even a biopsy is indicated [pdf], let alone an excision. Some FADs can actually regress on their own as well. The majority of cases in which non-suspicious FADs have been excised, therefore, tend to be at the request of the patient, or when the patient is aged 40 or older. Of course, any scan results that indicate any uncertainty about the lesion would be investigated a further through biopsy or excision.
So, what do FADs look like under the microscope?
Well, viewing them at low magnification first of all, their characteristic epithelial and stromal components can be clearly seen:
The epithelium lines glandular-looking structures, which are immediately surrounded by pale loose connective tissue. Dense pink (eosinophilic) bands of collagen can also be seen dividing the groups of glands.
In that first image, you may notice that the ducts actually appear distorted and elongated. This is a common FAD growth pattern known as an intracanalicular pattern.
A quick scan over another section of the slide reveals the other growth pattern that is found in most FADs; the pericanalicular pattern:
This pericanalicular pattern, as you can see, presents as small, rounded ducts. There’s no distortion here, it all seems very regular. The two growth patterns, therefore, are very easily distinguished between. They are often found within the same lesion, too, but the intracanalicular pattern is more commonly seen in larger FADs.
These features are so characteristic of FAD that no one would blame you for being convinced by just these two slides that what we’re looking at is a FAD. And you’d be right. But!… as nothing is ever simple, there is one major differential diagnosis that we must rule out, and that’s a phyllodes (pronounced phil-oy-deez) tumour, particularly if we’re examining a large breast lump that has recently rapidly grown.
The reason this is important is because phyllodes does have a sneaky tendency towards behaving like a malignant lesion. They have a high risk of recurrence and can even metastasise. On diagnosing a phyllodes tumour, the recommendation would then be for the surgeon to excise more of the surrounding breast tissue that once encapsulated the mass. By excising a wider margin, the risk of recurrence at that site is reduced immensely.
If the lump isn’t a rip-roaringly obvious suspicious lesion, the subtle differences we need to note in ruling out phyllodes are:
- presence/absence of overcrowded atypical spindle cells (sort of thin petal- or cigar-shaped cells) in the stromal component
- the pattern of proliferation around the elongated ducts
FADs do not contain overcrowding of spindle cells, and they present with rounded, or nodular, bulges that the ducts elongate around, as seen here:
In phyllodes tumour, overcrowding of atypical spindle cells are present, and the stromal proliferation is less smooth and rounded; it’s said to be “leaf-like” in shape. Click here to see a good example of the raggedy leafy proliferation in phyllodes tumour. Yes, they do look incredibly similar, so it’s important to correlate with other features. Besides, to an experienced pathologist’s eyes, it’s much easier to spot – that’s part of why they get paid so well!
So, we can safely say now that this lesion we’re looking at in these photomicrographs is definitely an FAD and not a phyllodes tumour.
I’ve seen you somewhere before
If you read the previous HistoQuarterly on normal breast, you may recall the image of what normal breast ducts look like. Well, here’s a recap if not:
Now let’s take a closer look at the epithelial layer in the ducts of the fibroadenoma:
Exactly the same cell composition; cuboidal epithelium (albeit a little squashed in the areas of stretched ducts), surrounded by basement membrane and myoepithelial cells.
On the edge
One last FAD feature we can take a look at is the very edge of the lump. Macroscopically, these lumps are smooth with some gentle lobulations. They are very easy for the surgeon to remove; so easy that the surrounding fatty breast tissue can be completely spared during excision. The procedure (please note that footage contains nudity and is possibly NSFW) is a bit like nudging your last Minstrel upwards and out through the packet.
And here’s what that outer edge looks like microscopically:
It’s basically a compact sheath of dense connective tissue. The black mess in the top right corner is from where I inked the specimen at the dissection bench. This helps the pathologist confidently assess the edges of the lump.
The edges (or “resection margins”) represent the point at which the specimen has been excised from the patient. That means the tissue beyond that margin (the empty space we see here) is still inside the patient. So, if the pathologist identifies any suspect pathology close to the ink, such as an infiltrating carcinoma for example, they will inform the clinician and advise the surgeon to re-excise the area containing the incidental pathology. This second piece of tissue would also be examined microscopically, and the process repeated until the margins became clear of pathology, or until other treatment pathways were sought.
All images are Copyright © 2014 Della Thomas.
FAD hits the news, July 2014: Multi-disciplinary research team discovers that a gene known as MED12 is altered in nearly 60 percent of fibroadenomas
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