Malignant Breast Disease

Before considering the histopathology, it is good to have a working understanding of what the normal breast architecture comprises.  Here is a slide showing normal breast tissue:

The arrows labelled ‘a’ mark the periphery of a cluster of ducts known as a lobule.  The arrows labelled ‘b’ point to some of the individual ducts also called acini which have a bilayered lining of inner epithelial and outer myoepithelial cells.  The surrounding pink material between these ducts is the intralobular stroma and outwith the lobule is the interlobular stroma.  Some adipose (fat) cells are seen at the left of the image.

Breast cancer is the commonest cancer in women and there is approximately a 1 in 8 chance that a woman will be diagnosed with breast cancer during her lifetime.

From the above list we can see that clonal proliferations of malignant cells in breast cancer arise when there are multiple genetic mutations which result from environmental and hormonal exposures and also with inherited mutations in tumour suppressor genes that increase susceptibility.  Around 12% of breast cancers are linked to heritable genes.  The main susceptibility genes known for familiar breast cancer are BRCA1, BRCA2, TP53 and CHEK2.  These are all tumour suppressor genes and if a defective copy of one is inherited then a sporadic mutation in the remaining allele leads to loss of tumour suppression and development of breast cancer.

The vast majority of breast cancers are sporadic and increased risk of these is largely linked to hormonal exposure.  Oestrogen is a promotor of breast cancer and so earlier menarche and increased number of menstrual cycles increases risk as does taking oestrogen longterm as part of hormone replacement therapy post-menopausally with risk increasing cumulatively with the duration of treatment.  Once mutations have occurred and pre-malignant or malignant cells are present, oestrogen stimulates and promotes their growth and division so they proliferate and also promote the surrounding stromal cells to alter in a way to support tumorigenesis.

Be aware that breast cancer can occur in men but the incidence is only 1% of that in women.  The risk factors are similar with family history, exposure to oestrogens and radiation being important, as well as an association with Klinefelter’s syndrome.  Inherited male breast cancer is most commonly associated with the BRCA2 gene.

 

 

Similar to benign breast disease, patients can present with a wide variety of symptoms including a breast lump, induration or inflammation of the overlying skin, nipple discharge, pain, inversion of the nipple, distortion of the breast or asymptomatically via the breast screening programme.  The GP can refer symptomatic patients to the breast triple assessment clinic.

In Scotland, women between the ages of 50 and 70 years old are offered breast screening every three years.  Women over 70 years old may attend via self-referral.  This involves attending for mammography which can pick cancer up at an early stage when it is still too small to palpate.  The aim is to find breast cancers at an in situ or early invasive stage and amenable to curative treatment to reduce the numbers of patients dying from breast cancer.

This picture shows a mammographic abnormality:

The yellow arrows show the dense area of carcinoma and the pink arrow points to the bright white calcifications at the centre which form from calcium deposits from necrotic cells.

If a mammographic abnormality is detected (or if symptoms or clinical signs were noted at screening appointment) the patient will be asked to attend further assessment in the form of a Triple Assessment Clinic with clinical examination, ultrasound (+further imaging as required) and core needle biopsy.  Core biopsy can be done under ultrasound guidance and will remove a length of tissue which can be sent to the pathology lab for assessment.  During this procedure a small metal marker can be inserted and further x-ray imaging can be performed to ensure the correct area was sampled.  The patient ends up with an E score graded 1 to 5 based on normal to highly suspicious examination, and a similar U score for ultrasound appearance.  The pathologist grades the core biopsy with a B score as follows:

These scores are correlated and discussed at MDT and a management plan is produced.  In the case of malignancy, often a wide local excision is recommended, to attempt to remove the entire tumour with minimal disfigurement.  If the tumour is very extensive then mastectomy may be required.

What do pathologists do with the tissue once it reaches the laboratory?

The first tissue we will assess is from a needle core biopsy which provides are thin slither of tissue removed with a vacuum assisted needle. This is taken as part of the triple test at initial assessment. This tissue is fixed in formalin, embedded in a wax block,  and then very thin slices are cut through it  so it can be placed on a slide for a pathologist to look at with a microscope.  It is stained with Haematoxylin and Eosin to make the cells look pink and blue so the cells and their architectural pattern can be easily visible for assessment.  The pathologist looks to see if the tissue shows any benign abnormality, any atypical cells or any in situ or invasive malignancy.  As discussed before this will be given a B score to help plan further patient management.

If a malignancy is detected the first line of treatment is usually wide local excision (WLE).  This lumpectomy is sent to the lab and preserved in formalin.  We paint different colours of ink on the edges of the specimen to help us to orient the different margins so we can report the clearance distance to each margin (anterior, posterior, lateral, medial, superior and inferior.  If any margin is involved by malignant cells then the surgeons can re-operate and take further shaves of tissue from the remaining tissue adjacent to the reported involved margin.  Here is a picture showing a slice of a WLE that has been prepared in this way:

 

 

This refers to a proliferation of neoplastic epithelial cells that are confined to ducts and lobules and have not spread beyond the basement membrane.  DCIS is given a score of B5a on core biopsy.  It has the appearance of the clonal population of cells expanding a duct but the myoepithelial cells can still be seen around the periphery indicating preservation of the basement membrane.  Clinically only 5% of carcinomas are detected while in situ, however screening increases this figure to around 25% detecting at the DCIS stage.  It can be seen as calcifications on mammography, or sometimes due to the periductal fibrosis which surrounds DCIS being seen as a mammographic density.   DCIS tends to involve one duct system.  DCIS is often treated with Wide Local Excision but if extensive then a mastectomy may be required.

Here is a further histological image of DCIS:

The pink clump of dead cells and debris in the image is comedo-necrosis.

DCIS architecture can either be solid, or cribriform (if lots of punched out spaces) or micropapillary (if lots of fingerlike strands of cells arranged in complex intraductal patterns).

The following image illustrates this condition using a cytokeratin immunohistochemical stain to highlight the malignant cells:

 

Lobular Carcinoma in Situ is another clonal proliferation of cells seen predominantly in lobules.  It differs from ductal carcinoma in situ by its tumour cell genetics and has a different histological appearance.  The cells are discohesive and this is likely due to the loss of E-Cadherin which is a tumour suppressive adhesion protein.  A pathologist often requests E-cadherin immunohistochemistry to confirm the diagnosis.

The malignant cells expand the lobules as a monotonous clonal population.  The cells are regularly spaced, discohesive, round to ovoid, small, with clear cytoplasm often containing intracytoplasmic mucin vacuoles.

Here is a picture of LCIS:

LCIS is a marker of increased risk of developing breast carcinoma.  Around 30% of women with LCIS will go on to develop invasive carcinoma over a period of 30years.  This can be NST, invasive lobular carcinoma or other special types.   However, unlike DCIS, the risk after LCIS is for either breast rather than the one where LCIS was discovered.

The following table summarises the histological differences between LCIS and DCIS:

Histology	LCIS	DCIS
Cellular features	Small, round, inconspicuous nucleoli	Variable, depending on nuclear grade.  Pleomorphic
Cellular cohesiveness	Discohesive	Cohesive
Architectural Pattern	Monotonous, diffusely obliterates most of lumen	Patterns include solid, cribriform, comedo, papillary
E-cadherin staining	Loss of staining (so negative)	Positive

Invasive breast cancer is that which has spread beyond the basement membrane to the surrounding stroma, invading surrounding tissues and structures.  By far the commonest variant of invasive breast cancer is known as ‘Invasive carcinoma of No Special Type’ (NST).  This means that less than 50% of the tumour is made up of a special type of breast cancer.  NST makes up around 80% of all invasive breast cancers.  If a tumour is made of more than 90% of a classical morphology with particular defined histological features, then it can be categorised as a ‘special type’ breast cancer.  Lobular Carcinoma is the commonest special type and makes up aound 10% of all invasive breast cancers.  The other 10% of invasive breast cancers consists of special types like tubular, cribriform, mucinous, medullary-like, micropapillary and metaplastic, mentioned here so you have an awareness that these rarer types exist.

The Royal College of Pathologists produces a Guideline of what information must be included to standardise the reporting of breast cancer.  We decide which type of carcinoma we have by looking at its morphology, then consider factors that show how the tumour may behave.  As well as detecting the type of cancers, pathologists must also determine the grade (an important prognostic indicator).

Grading is assessment of differentiation of the tumour (this means how closely it resembles the tissue of origin, in this case how similar it is to normal breast tissue).

The NPI (Nottingham Prognostic Index) is just that score we give at the end of the report. It’s called Breast cancer grading (Nottingham criteria) that we use for grading.

Firstly, this involves assessing differentiation (how well a tissue resembles its normal parent tissue) in terms of acinar formation:  >75% of malignant cells forming tubules scores 1, 10-75% scores 2 and <10% scores 3.

Secondly we consider nuclear atypia which takes into account nuclear size and pleomorphism scoring 1, 2 and 3.

Thirdly we do a mitotic count over 10 High Power Fields and this also scores either 1, 2 or 3 moving from least to most mitoses.

The total from the scores is then used to give the grade:

Scores 3-5 = Grade 1

Scores 6 or 7 = Grade 2

Scores 8 or 9 = Grade 3

The grade gives a good guide to prognosis, with Grade 1 having a better survival rate compared to Grade 3.

For invasive malignancy we will give a tumour stage as well, based on TNM guidelines.  Staging differs from grading in that it is the measure of the size the tumour has grown to and how far it has spread through the body, be it into adjacent tissues or distant organs.

pT1 is less than or equal to 2mm diameter, pT2 is 2-5mm, pT3 is >5mm, and pT4 is carcinoma that has spread to skin epidermis or chest wall.  Note that inflammatory breast cancer also falls into pT4 as it is a diffusely infiltrative subtype with a very poor prognosis.

Nodal score – pN0 means no spread to regional lymph nodes and then there are pN1, 2 and 3 scores based on number of involved nodes.

Metastases cannot be assessed by a pathologist on the resection specimen but this information can be collated at the MDT using the information from the radiologists and clinicians.

As a further prognostic indicator we also report whether lymphovascular invasion has occurred, as once tumour is within vessels it can travel to other parts of the body.

Remember these invasive NST tumours show less than 50% of special type characteristics.  They account for the majority of invasive breast carcinomas (around 80%).  Their morphology is variable in terms of the tumour margin, cytonuclear appearance, growth pattern (architecture), tumour marker biology and whether or not they have a lymphoid reaction.

There is no evidence of any special differentiation here – no tubules, no mucin production etc.  In the centre of the image the cell with the very dark elongated nuclei is one of a number of mitoses (cell in process of division to replication) which is evidence that the tumour is expanding and the large number of mitoses suggests this is an uncontrolled proliferation.

 

 

This is the most commonly seen special type of breast carcinoma and accounts for approximately 10% of all breast carcinomas.

This carcinoma consists of small monotonous cells, frequently with intracytoplasmic lumina, which are identical to the cells seen in LCIS.  They are discohesive and often line up in files or form a targetoid pattern around ducts.  As with LCIS, these cells lose e-cadherin staining and they tend to be ER and PR positive and HER-2Negative.

This image shows the classic discohesive pattern of cells and on the right side of the image, it shows the filing pattern with cells in lines.  This can spread insidiously and can be hard to spot as the following picture demonstrates:

Lobular carcinoma can infiltrate the breast tissue widely without stromal reaction which is another reason it can be hard to detect on mammogram.  Also there is a risk that it may be present bilaterally and so women can have an MRI scan which better detects lobular carcinoma prior to having surgical resection.

 

Luminal A subtypes tend to be ER positive, PR positive and HER2 negative.

Luminal B subtypes tend to be ER positive, PR positive or negative and HER2 negative. They are often more poorly differentiated than luminal A subtypes and have a worse prognosis than luminal A.

HER2 amplified tends to be HER2 positive and both ER, PR negative.

Basal-like tend to be triple negative (ER, PR and HER2 negative).

This information is used by clinicians to determine the treatment plan for patients. For example patients with ER positive cancers are often given endocrine therapies such as tamoxifen.  Patients with Her-2 positive cancers  may be given Herceptin.  Patients with basal-like cancers will not respond to endocrine therapy or herceptin and so are more likely to be given chemotherapy.

They will also assess for lymph node metastases.  Decision making for patient management is based upon these assessments.  The pathologist will attend the MDT along with the radiologists, breast surgeons and oncologists and an individualised treatment plan for the patient will be discussed.

Once in the vascular system the breast cancer cells typically metastasize to bone, lung and liver and brain.

We also include information on receptor status in the report as per Royal College of Pathology guidelines.  We perform immunohistochemistry (IHC) and Fluorescence In-Situ Hybridisation (FISH) so that we can tell the clinicians the hormonal receptor status of the tumour which helps to guide the treatment the patient is offered.  We measure Oestrogen Receptor status (ER), Progesterone Receptor status (PR) and a Human Epidermal Growth factor Receptor called Herceptin 2 (HER-2) status.  We do this by using brown dye labelled antibodies against each receptor type and looking to see if there is any staining after incubating the antibody with a section of the tumour.

If, as shown above, there is a large proportion of strongly staining oestrogen receptors in the tumour, the patient will be offered a medication that blocks oestrogen receptor as part of their treatment to help to stop the tumour growing.

If the HER-2 IHC is equivocal then we will use FISH testing where the Herceptin2 gene is labelled with a fluorescent probe so we can count the number of copies it has and we compare this to the number of copies of another gene, enabling us to determine if the HER2 gene is amplified (if the ratio is >2).

The above image shows a typical appearance of what we see down a microscope slide during FISH assessment.  The Her2 gene probe is red while the green dots are attached to copies of Chromosome 17.

So for the 25% of patients whose tumour cells express excessive amounts of HER2 we can prescribe them Herceptin treatment which has significantly improved survival rates for these patients.

Well done!  You have reached the end of this CAL!  Hopefully you now have better knowledge and understanding of breast malignancy and the role of pathologists in diagnosing and reporting it, so the MDT can plan further management of the patients.  Here are a few quick quiz questions so you can check your recall.