Breast cancer for students.

1. Breast Cancer
Annia Ramos Pérez
Consultant General Surgeon.

2. Epidemiology
 Breast cancer is the most common site-specific cancer in
women and is the leading cause of death from cancer for
women age 20 to 59 years.
 Women living in less industrialized nations tend to have
a lower incidence of breast cancer than women living in
industrialized countries.

3. Natural History/Primary Breast Cancer.
 More than 80% of breast cancers show productive fibrosis
that involves the epithelial and stromal tissues.
 With growth of the cancer and invasion of the surrounding
breast tissues, the accompanying desmoplastic response
entraps and shortens Cooper’s suspensory ligaments to
produce a characteristic skin retraction.
 Localized edema (peau d’orange) develops when drainage of
lymph fluid from the skin is disrupted.

4. Natural History/Primary Breast Cancer.
 With continued growth, cancer cells invade the skin, and
eventually ulceration occurs.
 As new areas of skin are invaded, small satellite nodules
appear near the primary ulceration.

5. Axillary Lymph Node Metastases.
 As the size of the primary breast cancer increases, some
cancer cells are shed into cellular spaces and transported
via the lymphatic network of the breast to the regional
lymph nodes, especially the axillary lymph nodes.
 Lymph nodes that contain metastatic cancer are at first ill-
defined and soft but become firm or hard with continued
growth of the metastatic cancer.
 Eventually the lymph nodes adhere to each other and
form a conglomerate mass.

6. Axillary Lymph Node Metastases.
 Cancer cells may grow through the lymph node capsule and fix
to contiguous structures in the axilla, including the chest wall.

7. Axillary Lymph Node Metastases
 Typically, axillary lymph nodes are involved
sequentially from the low (level I) to the central (level
II) to the apical (level III) lymph node groups.
 Women with node-negative disease had less than a
30% risk of recurrence, compared with as much as a
75% risk for women with node-positive disease.

8. Distant Metastases.
 At approximately the 20th cell doubling, breast cancers
acquire their own blood supply (neovascularization).
 Thereafter, cancer cells may be shed directly into the
systemic venous blood to seed the pulmonary circulation
via the axillary and intercostal veins or the vertebral
column via Batson’s plexus of veins, which courses the
length of the vertebral column.
 These cells are scavenged by natural killer lymphocytes
and macrophages.

9. Distant Metastases.
 Successful implantation of metastatic foci from breast cancer
predictably occurs after the primary cancer exceeds 0.5 cm in
diameter, which corresponds to the 27th cell doubling.
 For 10 years after initial treatment, distant metastases are the
most common cause of death in breast cancer patients.

10. Distant Metastases.
 For this reason, conclusive results cannot be derived from breast
cancer trials until at least 5 to 10 years have elapsed.
 Although 60% of the women who develop distant metastases will
do so within 60 months of treatment, metastases may become
evident as late as 20 to 30 years after treatment of the primary
cancer.

11. Distant Metastases.
 Common sites of involvement, in order of frequency, are
bone, lung, pleura, soft tissues, and liver.

12. HISTOPATHOLOGY OF BREAST CANCER/Carcinoma
In Situ
 Cancer cells are in situ or invasive depending on whether or not
they invade through the basement membrane.
 Multicentricity refers to the occurrence of a second breast cancer
outside the breast quadrant of the primary cancer (or at least 4
cm away), whereas multifocality refers to the occurrence of a
second cancer within the same breast quadrant as the primary
cancer (or within 4 cm of it).

13. BREAST CANCER/ RISK FACTORS
Conventional factors(not modifiable):
 Age. It is rare before the age of 25
 Genetic factors: BRCA1 y BRCA2
 Hormonal factors: nulliparity, late menopause, early menarche,
first full-term pregnancy after age 30, poor or no lactation and
the use of oral contraceptives
External factors (modifiable):
 Obesity
 Type of alimentation
 Smoking habit
 Night work

15. HISTOPATHOLOGY OF BREAST
CANCER/Carcinoma In Situ
 Multicentricity occurs in 60% to 90%
of women with LCIS, whereas the
rate of multicentricity for DCIS is
reported to be 40% to 80%.
 LCIS occurs bilaterally in 50% to 70%
of cases, whereas DCIS occurs
bilaterally in 10% to 20% of cases.

16. Lobular Carcinoma In Situ
 LCIS originates from the terminal duct lobular
units and develops only in the female breast.
 LCIS has a distinct racial predilection, occurring
12 times more frequently in white women than
in African-American women.

17. Ductal Carcinoma In Situ.
 Although DCIS is predominantly seen in
the female breast, it accounts for 5% of
male breast cancers.
 Histologically, DCIS is characterized by a
proliferation of the epithelium that lines
the minor ducts, resulting in papillary
growths within the duct Lumina.

18. HISTOPATHOLOGY OF BREAST
CANCER/Carcinoma In Situ

19. DIAGNOSIS OF BREAST CANCER
In ∼30% of cases, the woman discovers a lump in her
breast.
Other less frequent presenting signs and symptoms of
breast cancer include:
(a) Breast enlargement or asymmetry
(b) Nipple changes, retraction, or discharge
(c) Ulceration or erythema of the skin of the breast
(d) Axillary mass
(e) Musculoskeletal discomfort.

20. DIAGNOSIS OF BREAST CANCER
 However, up to 50% of women presenting
with breast complaints have no physical
signs of breast pathology. Breast pain
usually is associated with benign disease.

22. Examination/ Inspection.
 The clinician inspects the woman’s breast with her arms by her
side, with her arms straight up in the air, and with her hands on
her hips (with and without pectoral muscle contraction).
 Symmetry, size, and shape of the breast are recorded, as well as
any evidence of edema (peau d’orange), nipple or skin
retraction, or erythema.
 With the arms extended forward and in a sitting position, the
woman leans forward to accentuate any skin retraction.

23. Examination/ Inspection/ Palpation

24. Palpation.
 As part of the physical examination, the
breast is carefully palpated.
 With the patient in the supine position,
the clinician gently palpates the breasts,
making certain to examine all quadrants
of the breast from the sternum laterally
to the latissimus dorsi muscle and from
the clavicle inferiorly to the upper rectus
sheath.

25. Palpation.
 The examination is performed with the
palmar aspects of the fingers, avoiding
a grasping or pinching motion.
 The breast may be cupped or molded in
the examiner’s hands to check for
retraction.
 A systematic search for
lymphadenopathy then is performed.

26. Palpation.
 By supporting the upper arm and elbow, the
examiner stabilizes the shoulder girdle.
 Using gentle palpation, the clinician assesses all
three levels of possible axillary lymphadenopathy.
 Careful palpation of supraclavicular and parasternal
sites also is performed.

27. Palpation.
 A diagram of the chest and contiguous
lymph node sites is useful for recording
location, size, consistency, shape, mobility,
fixation, and other characteristics of any
palpable breast mass or lymphadenopathy

28. INVESTIGATIONS FOR BREAST CANCER

29. Imaging Techniques/Mammography.
 With screening mammography, two views of the breast are
obtained:
1. The cranio-caudal (CC) view
2. The medio-lateral oblique (MLO)
 The MLO view images the greatest volume of breast tissue, including
the upper outer quadrant and the axillary tail of Spence.

30. Imaging Techniques/Mammography
 Compared with the MLO view, the CC view provides better
visualization of the medial aspect of the breast and
permits greater breast compression.

31. Imaging Techniques/Mammography

32. Imaging Techniques/Mammography.
 Screening mammography is used to detect
unexpected breast cancer in asymptomatic
women.
 Diagnostic mammography is used to evaluate
women with abnormal findings such as a breast
mass or nipple discharge.
 Mammography also is used to guide
interventional procedures, including needle
localization and needle biopsy.

33. Imaging Techniques/Mammography.
 Specific mammographic features that suggest a diagnosis of
breast cancer include a solid mass with or without stellate
features, asymmetric thickening of breast tissues, and
clustered micro-calcifications.
 The presence of fine, stippled calcium in and around a
suspicious lesion is suggestive of breast cancer and occurs in
as many as 50% of nonpalpable cancers.

34. Imaging Techniques/Mammography.
 These micro-calcifications are an especially important sign
of cancer in younger women, in whom it may be the only
mammographic abnormality.

36. Ductography.
 The primary indication for ductography is
nipple discharge, particularly when the fluid
contains blood.
 Radiopaque contrast media is injected into one
or more of the major ducts, and mammography
is performed.
 Intraductal papillomas are seen as small filling
defects surrounded by contrast media
 Cancers may appear as irregular masses or as
multiple intraluminal filling defects.

37. Ultrasonography.
 Ultrasonography is an important method of
resolving equivocal mammographic findings,
defining cystic masses, and demonstrating the
echogenic qualities of specific solid
abnormalities.
 On ultrasound examination, breast cysts are
well circumscribed, with smooth margins and
an echo-free center.

38. Ultrasonography.
 Ultrasound image of the mass shows it to
be anechoic with a well-defined back
wall, characteristic of a cyst

39. Ultrasonography.
 Benign breast masses usually show smooth
contours, round or oval shapes, weak
internal echoes, and well-defined anterior
and posterior margins.
 Breast cancer characteristically has irregular
walls but may have smooth margins with
acoustic enhancement.

41. Ultrasonography.
Ultrasonography is used to guide fine-needle aspiration
biopsy, core-needle biopsy, and needle localization of breast
lesions.
Its findings are highly reproducible, and it has a high patient
acceptance rate, but it does not reliably detect lesions that
are ≤1 cm in diameter.
Ultrasonography can also be utilized to image the regional
lymph nodes in patients with breast cancer.

42. Magnetic Resonance Imaging.
 There is current interest in the use of MRI to
screen the breasts of high-risk women and of
women with a newly diagnosed breast cancer.
 In the first case, women who have a strong
family history of breast cancer or who carry
known genetic mutations require screening at an
early age because mammographic evaluation is
limited due to the increased breast density in
younger women.

43. Magnetic Resonance
Imaging.
 In the second case, an MRI study of the
contralateral breast in women with a known
breast cancer has shown a contralateral
breast cancer in 5.7% of these women.
 MRI can also detect additional tumors in the
index breast (multifocal or multicentric
disease) that may be missed on routine
breast imaging and this may alter surgical
decision.

44. Breast Biopsy/Nonpalpable Lesions.
 Image-guided breast biopsy specimens are
frequently required to diagnose nonpalpable
lesions.
 The combination of diagnostic mammography,
ultrasound or stereotactic localization, and fine-
needle aspiration (FNA) biopsy achieves almost
100% accuracy in the preoperative diagnosis of
breast cancer.

45. Breast Biopsy/Nonpalpable Lesions.
 Core-needle biopsy is preferred over open
biopsy for nonpalpable breast lesions
because a single surgical procedure can be
planned based on the results of the core
biopsy.

46. Palpable Lesions
 FNA or core biopsy of a palpable breast
mass can usually be performed in an
outpatient setting.

47. BREAST CANCER STAGING
 The clinical stage of breast cancer is
determined primarily through physical
examination of the skin, breast tissue,
and regional lymph nodes (axillary,
supraclavicular, and internal
mammary).
 However, clinical determination of
axillary lymph node metastases has an
accuracy of only 33%.

48. BREAST CANCER STAGING
 Ultrasound (US) is more sensitive than physical
examination alone in determining axillary lymph
node involvement during preliminary staging of
breast carcinoma.
 FNA or core biopsy of sonographically
indeterminate or suspicious lymph nodes can
provide a more definitive diagnosis than US alone.

49. BREAST CANCER STAGING
 A frequently used staging system is the TNM
(tumor, nodes, and metastasis) system.
 The American Joint Committee on Cancer
(AJCC) has recently modified the TNM system
for breast cancer to include both anatomic and
biologic factors.
 Pathologic stage combines the findings from
pathologic examination of the resected primary
breast cancer and axillary or other regional
lymph nodes.

50. BREAST CANCER STAGING

51. BREAST CANCER STAGING

52. BREAST CANCER STAGING

53. BREAST CANCER STAGING

54. BREAST CANCER STAGING

55. Biomarkers
 Breast cancer biomarkers are of
several types.
 Risk factor biomarkers are those
associated with increased cancer
risk.

57. Steroid Hormone Receptor Pathway
 Hormones play an important role in the development and progression
of breast cancer.
 Estrogens, estrogen metabolites, and other steroid hormones such as
progesterone all have been shown to have an effect.
 Breast cancer risk is related to estrogen exposure over time.
 In postmenopausal women, hormone replacement therapy consisting of
estrogen plus progesterone increases the risk of breast cancer by 26%
compared to placebo.

58. BREAST CANCER THERAPY

59. OVERVIEW OF BREAST CANCER THERAPY
 Before diagnostic biopsy, the surgeon must consider the possibility
that a suspicious mass or mammographic finding may be a breast
cancer.
 Once a diagnosis of breast cancer is made, the type of therapy offered
to a breast cancer patient is determined by the stage of the disease,
the biologic subtype, and the general health status of the individual

60. OVERVIEW OF BREAST CANCER THERAPY
 Laboratory tests and imaging studies are performed based on the
initial stage.
 Before therapy is initiated, the patient and the surgeon must share a
clear perspective on the planned course of treatment.
 Before initiating local therapy, the surgeon should determine
appropriate the clinical stage, histologic characteristics and
biomarker levels.

61. OVERVIEW OF BREAST CANCER THERAPY

62. In Situ Breast Cancer (Stage 0)/ LCIS
 Bilateral mammography is performed to determine the
extent of the in situ cancer and to exclude a second
cancer.
 Because LCIS is considered a marker for increased risk
rather than an inevitable precursor of invasive disease,
the current treatment options for LCIS include
observation, chemoprevention, and bilateral total
mastectomy.
 The goal of treatment is to prevent or detect at an early
stage the invasive cancer that subsequently develops in
25% to 35% of these women.

63. In Situ Breast Cancer (Stage 0)/ LCIS
 There is no benefit to excising LCIS because the disease
diffusely involves both breasts in many cases and the
risk of developing invasive cancer is equal for both
breasts.
 The use of tamoxifen as a risk-reduction strategy should
be considered in women with a diagnosis of LCIS.

64. In Situ Breast Cancer (Stage 0)/ DCIS
 Women with DCIS and evidence of extensive
disease (>4 cm of disease or disease in more than
one quadrant) usually require mastectomy.
 For women with limited disease, lumpectomy and
radiation therapy are generally recommended.
 For nonpalpable DCIS, needle localization or other
image-guided techniques are used to guide the
surgical resection.

65. In Situ Breast Cancer (Stage 0)/ DCIS
Specimen mammography is performed to ensure
that all visible evidence of cancer is excised.
Adjuvant tamoxifen therapy is considered for DCIS
patients with ER-positive
Magnification view of calcifications. Due to the
extent of the disease the patient is not a good
candidate for breast conserving surgery.

66. Early Invasive Breast Cancer (Stage I, IIA, or IIB)
 There have been six prospective randomized trials comparing
breast-conserving surgery to mastectomy in early stage breast
cancer, and all have shown equivalent survival rates regardless of
the surgical treatment type.
 The findings of that researches supported the use of lumpectomy
and radiation therapy in the treatment of stages I and II breast
cancer and this has since become the preferred method of
treatment for women with early stage breast cancer who have
unifocal disease and who are not known BRCA mutation carriers.

67. Advanced Local-Regional Breast Cancer
(Stage IIIA or IIIB)
 Women with stage IIIA and IIIB breast cancer have
advanced local-regional breast cancer but have no
clinically detected distant metastases
 In an effort to provide optimal local-regional disease-
free survival as well as distant disease-free survival
for these women, surgery is integrated with radiation
therapy and chemotherapy

68. Advanced Local-Regional Breast Cancer
(Stage IIIA or IIIB)
 However, it should be noted that these patients have an
increased risk of distant metastasis that is often
highlighted by radiological evidence when staging PET or
CT and bone scans are performed.
 Thus, the paradigm for small screen detected cancers
where cure can be expected in >90% of patients, often by
local treatment alone, is not appropriate for patients with
locally advanced disease.

69. Advanced Local-Regional Breast Cancer
(Stage IIIA or IIIB)
 Preoperative (also known as neo-adjuvant) chemotherapy
should be considered in the initial management of patients with
locally advanced stage III breast cancer, especially those with
estrogen receptor negative tumors.
 Chemotherapy is used to maximize distant disease-free survival,
whereas radiation therapy is used to maximize local-regional
control and disease-free survival.
 In selected patients with stage IIIA cancer, preoperative
chemotherapy can reduce the size of the primary cancer and
permit breast-conserving surgery.

70. Advanced Local-Regional Breast Cancer
(Stage IIIA or IIIB)

71. Advanced Local-Regional Breast Cancer
(Stage IIIA or IIIB)

72. Distant Metastases (Stage IV)
 Treatment for stage IV breast cancer is not
curative but may prolong survival and enhance
a woman’s quality of life.
 Endocrine therapies that are associated with
minimal toxicity are preferred to cytotoxic
chemotherapy in ER-positive disease.
 Symptoms per se (e.g., breathlessness) are not
in themselves an indication for chemotherapy.

73. Distant Metastases (Stage IV)
 For example, breathlessness due to a pleural
effusion can be treated with percutaneous
drainage, and if the breathlessness is relieved,
the patient should be commenced on endocrine
therapy.
 If the breathlessness is due to Lymphangitic
spread, then chemotherapy would be the
treatment of choice.

74. Distant Metastases (Stage IV)
 Women with stage IV breast cancer may develop anatomically localized
problems that will benefit from individualized surgical or radiation treatment,
such as:
 Brain metastases
 Pleural effusion
 Pericardial effusion
 Biliary obstruction
 Ureteral obstruction
 Impending or existing pathologic fracture of a long bone
 Spinal cord compression
 Painful bone or soft tissue metastases

75. SURGICAL TECHNIQUES IN BREAST CANCER

76. Excisional Biopsy With Needle Localization
 Excisional biopsy implies complete removal of a
breast lesion with a margin of normal
appearing breast tissue
 Needle-core biopsy is the preferred diagnostic
method, and excisional biopsy should be
reserved for those cases in which the needle
biopsy results are discordant with the imaging
findings or clinical examination.

77. Excisional Biopsy With Needle Localization
 Excisional biopsy with needle or seed localization
requires a preoperative visit to the mammography suite
for placement of a localization wire or a radioactive or
magnetic seed that can be detected intra-operatively
with a handheld probe.
 The lesion can also be targeted by sonography in the
imaging suite or in the operating room.
 The lesion to be excised is accurately localized by
mammography, and the tip of a thin wire hook or a
seed is positioned close to the lesion

78. Excisional Biopsy With Needle Localization
 Using the wire hook as a guide, or detection of
the seed with a handheld probe, the surgeon
subsequently excises the suspicious breast
lesion while removing a margin of normal-
appearing breast tissue.
 Before the patient leaves the operating room,
specimen radiography is performed to confirm
complete excision of the suspicious lesion

79. Excisional Biopsy With Needle Localization
Wire localization procedure. Mammographic image of
hook-wire in place targeting lesion for excision in the left
breast

80. Sentinel Lymph Node Dissection
 Sentinel lymph node (SLN) dissection is primarily used to assess the
regional lymph nodes in women with early breast cancers who are
clinically node-negative by physical examination and imaging
studies.
 This method also is accurate in women with larger tumors (T3 N0),
because nearly 75% of these women will prove to have axillary
lymph node metastases on histologic examination, and wherever
possible it is better to identify them preoperatively as this will allow
a definitive procedure for known axillary disease.

81. Sentinel Lymph Node Dissection
 Evidence from large prospective studies suggests that the
combination of intraoperative gamma probe detection of
radioactive colloid and intraoperative visualization of blue dye
(isosulfan blue dye or methylene blue) is more accurate for
identification of SLNs than the use of either agent alone.
 On the day before surgery, or the day of surgery, the radioactive
colloid is injected either in the breast parenchyma around the
primary tumor or prior biopsy site, into the sub-areolar region, or
sub-dermally in proximity to the primary tumor site.

82. Sentinel Lymph Node Dissection
 A hand-held gamma counter is used to trans- cutaneously identify the location
of the SLN.
 This can help to guide placement of the incision.
 A 3- to 4-cm incision is made in line with that used for an axillary dissection
 After dissecting through the subcutaneous tissue, the surgeon dissects through
the axillary fascia, being mindful to identify blue lymphatic channels.

83. Sentinel Lymph Node Dissection
 Following these channels can lead directly
to the SLN and limit the amount of
dissection through the axillary tissues.
 The gamma probe is used to facilitate the
dissection and to pinpoint the location of
the SLN.

84. Breast Conservation Surgery
Breast conservation involves resection of the primary breast cancer with
a margin of normal-appearing breast tissue, adjuvant radiation therapy,
and assessment of regional lymph node status
The quadrantectomy technique introduced by the Dr. Umberto Veronesi
(1925-2016) included the skin of the quadrant, the quadrant including the
aponeurosis of the pectoral at that level, resection of the pectoralis minor
and radical dissection of the armpit.
It is known as Umberto Veronesi's mastectomy

85. Breast Conservation Surgery
Selection criteria
There must be a consent of the patient after knowing the risk of local recurrence.
This requires:
Clinical history, physical examination.
Mammographic study
Good breast-tumor relation
Possibilities of radiant treatment after surgery
Possibilities of having a proper follow-up.

86. Breast Conservation Surgery
Absolute contraindications:
––Denial of the patient.
––No possibilities of radiation treatment.
–– No Possibility of mammography
–– No possibilities of having follow-up.
–– Multicentric tumors.
–– Extensive micro-calcifications.
–– Paget's disease with an underlying breast tumor
–– Inadequate relation between the breast and the tumor.
–– Extensive intra-ductal component (21% relapse).
–– Acute inflammatory breast cancer

87. Breast Conservation Surgery
Relative contraindications:
––Tumor size
––Multifocality
––Gestation
––Retro-areolar lesions.
---Advanced age.
––Very bulky breasts can allow good recovery surgical section, but
subsequent radiation therapy can have difficulties homogenizing
the necessary dose.
––Collagen diseases (lupus, scleroderma), which contraindicates
radiotherapy.

88. Modified radical (“Patey”) mastectomy
 A modified radical (“Patey”) mastectomy removes all
breast tissue, the nipple-areola complex, skin, and the
levels I, II, and III of axillary lymph nodes.
 The pectoralis minor that was divided and removed by
Patey may be simply divided, giving improved access to
level III nodes, and then left in situ.
 Elevation of skin flaps. Skin flaps are 7 to 8 mm in
thickness, inclusive of the skin and tela subcutanea.

89. Modified radical (“Patey”) mastectomy
Modified radical mastectomy after
resection of breast tissue.
The pectoralis major muscle is cleared of its fascia as the
overlying breast is elevated.
The latissimus dorsi muscle is the lateral boundary of the
dissection

90. RADICAL “HALSTED” MASTECTOMY

91. NONSURGICAL BREAST CANCER
THERAPIES/Radiation Therapy
 Radiation therapy is used for all stages of breast cancer dependi
on whether the patient is undergoing BCT or mastectomy.
• Postoperative radiotherapy, if chemotherapy is used, should
be started before 7 months after the surgery.
• In case of not offering chemotherapy, the moment ideal to
start radiotherapy will be before 8 weeks after surgery.

92. Adjuvant Chemotherapy

93. Antiestrogen Therapy/Tamoxifen.
 The most widely studied hormone receptors are the estrogen
receptor and progesterone receptor.
 After binding to estrogen receptors in the cytosol, tamoxifen
blocks the uptake of estrogen by breast tissue.
 Adjuvant therapy with tamoxifen for 5 years reduced breast
cancer mortality by about a third through the first 15 years of
follow-up

94. Aromatase Inhibitors
 In postmenopausal women, aromatase inhibitors are now
considered first-line therapy in the adjuvant setting

95. Anti-HER2 Therapy
 Pertuzumab
 Trastuzumab

96. Inflammatory Breast Carcinoma
 Inflammatory breast carcinoma (stage IIIB) accounts for <3% of breast cancers.
 This cancer is characterized by the skin changes of brawny induration, erythema
with a raised edge, and edema (peau d’orange).
 Surgery alone and surgery with adjuvant radiation therapy have produced
disappointing results in women with inflammatory breast cancer.
 However, Neoadjuvant chemotherapy with an anthracycline-containing regimen
may affect dramatic regressions in up to 75% of cases.

97. Inflammatory Breast Carcinoma

98. Bibliography
 Sabiston. Textbook of Surgery.
 Schwartz. Textbook of Surgery.
 General Surgery. Cuban Book for Students. Volume 3.

99. Bibliography
 Excisional Biopsy With Needle Localization: https://youtu.be/PuNoQ-sCJ54
 Sentinel Lymph Node Dissection: https://youtu.be/Cdl2JhhTfYc
 Modified radical mastectomy: https://youtu.be/3-QRGvctJVk
 Breast Conserving Surgery:
 https://youtu.be/lZBG2eLwJzk
 https://youtu.be/Ut6GwvDp7UA