BCG and psoriasis

There are multiple competing theories regarding the exact cause of psoriasis as well as several different types of psoriasis.  Mine happens to be plaque, but since I have arthritis, it may also be psoriatic.  The explanation that you provided I think is accurate and the T cells definitely play a major role.   The biologics (and there are so many that I've lost count) share the commonality of T-cell suppression to subdue the flares.  I only tried two (one was Otezla) and my body did not respond well so I quit this route and work with managing the symptoms. 

IMO, your hypothesis about the BCG versus the GEM/DOCE TX is correct.  When comparing the TX protocols for these two, it appears that the latter one has several advantages in terms of side effects , manageability and possibly efficacy.

I found another site that you might like if you're not already familiar with it.  It's loaded with resources.
Here is a sample: bcan.org/what-is-non-muscle-invasive-bladder-cancer/

Good readings and good points.   The key point is differences in how cells die when BCG instilled or GEM/DOC are instilled, how it can possible affect  your psoriasis. 

Is the following explanation of causing psoriasis correct?  I picked it up at this site.
 www.mypsoriasisteam.com/resources/t-cells-in-psoriasis-a-simplified-guide

"Psoriasis occurs when something goes wrong with your immune system. Your immune cells become overactive and attack your skin and joints. T cells, a type of immune cell, play an important role in  causing psoriasis ."

BCG treatment will invoke various immune cells, including T-cells which theoretically are supposed to attack only BCG infected cells, but these BCG invoked T-cells which circulate in blood seem to attack unrelated cells sometimes, which can cause flair to patients with autoimmune disease, i.e. the patient I know with rheumatic arthritis had flair after 4th BCG dose and ended up a week in hospital.

So, if psoriasis is caused by more T cells in the skin than usual, potentially BCG invoked T-cells further affect the condition of psoriasis.

On the hand, Gemcitabine and Docetaxel chemotherapy do not rely on or invoke T-cells to kill cancer cells.  It rely on our body's built in mechanism to destroy cell l when the cell fails to divide into two new cells in cell cycle.  This is called program death or apoptosis.   Gemcitabine prevents DNA to be replicated in early phase in the cell cycle  and Docetaxel prevents the cell to split into two new cells at the later phase in the cell cycle.  In both cases, our body lead the cell to death.  In this sense, Gemcitabine and Docetaxel treatment should not affect the condition of psoriasis.

Below are treatment protocols at BC Cancer Center for intravesical BCG and intravesical Gemcitabine and Docetaxel.
 
BCG
www.bccancer.bc.ca/chemotherapy-protocols-site/Documents/Genitourinary/GUBCG_Protocol.pdf

Notice Exclusions criteria include  "Concurrent systemic corticosteroids or a specific immunodeficiency syndrome"/

GEMCITABINE + DOCETAXEL
www.bccancer.bc.ca/chemotherapy-protocols-site/Documents/Genitourinary/GUBGEMDOC_Protocol.pdf

Notice that Exclusions criteria does not list any immune related matters.

BCG dose reduction and its side effects

In chemotherapy, dosage and efficacy and severity of side effects are usually linearly corelated, but BCG is not.   Due to the BCG shortage, in the US, dose reduction 1/2, 1/3 dose were recommended.  1/3 dose did not affect efficacy much in several studies.  In terms of side effects, some study said it reduced side effects but other studies said not much change in side effects.  I recall someone posted that he was going to reduce to 1/10 to complete maintenance phase.  Dr. Lamm said he would reduce to 1/10, 1/50 even to 1/100 to reduce side effects so patients can complete 3 years maintenance program.  But, for T1HG, initial 6 weeks induction treatment are recommended with full dose if available, indicating dosage can be reduced to 1/10 or  lower without affecting efficacy in the induction treatment.  If 1/3 dose has similar efficacy, it means that it is invoking sufficient amount of T-cells, indicating that 1/3 dose may affect psoriasis as much as full dose BCG does.  It is something your psoriasis doctor, urologist and you need to plan carefully if BCG treatment is selected.    

Thank you very much for your informative response.  I tapped into the pubmed site you mentioned and have spent several days and many hours downloading relevant articles and reading, rereading, and highlighting pertinent information.  My tumor was a high grade invasive papillary urothelial carcinoma of about 2.5 cm which I'm told is a medium sized tumor so I was looking for articles relevant to this situation. 

Here are a couple of good articles I found:  Medscape: Bladder Cancer Treatment Protocols updated 4/24, 2023, author Gary D. Steinberg, MD.;  BCG and autoimmunity: another two-edged sword (2001);  The one I really liked was from the Carver College of Medicine; Alternative bladder cancer treatment emerges amid worldwide shortage of standard of care BCG:  A combination of two inexpensive, readily available chemotherapy drugs performs better than BCG by Jennifer Brown, 2/28/23.
Another article I found very helpful was this one from the Cleveland Clinic:  Bacillus Calmette-Guerin (BCG) Treatment 
From the National Cancer Institute: For Common Form of Bladder Cancer, Chemo Combo Effective Alternative to BCG

At this moment, I am leaning towards either a reduced dosage of BCG or the gem/doce tx which some research suggests is more effective with fewer side effects than BCG.

Below is   BC Cancer Center in Vancouver, BC, Canada's  contraindications of intravesical BCG administration.  I understand some of it but not all.  

immune response, including positive HIV serology and immune suppressant therapy.
  - steroid therapy does not contraindicate administration if:< 2 weeks;< 20mg dose of prednisone or equivalent per day; alternate-day regiments of low-dose short-acting preparations; at physiologic doses for maintenance; topical ;inhaled; or intra-articular, bursal or tendon injection.
-  1 month should elapse before using in patients who have discontinued a >2 week regimen of high-dose systemic steroids, due to concern about the safety and possible reduced efficacy of live-organism preparations.

I know a male patient with rheumatic arthritis had big flair after 4th dose of 6 weeks  which required  a week long hospitalization. The BCG treatment was discontinued then.  The patient has not had recurrence over a year.

 I know another patient with autoimmune disease who stopped the treatment for autoimmune disease and received BCG.  The decision to pause the treatment for her Rheumatism was made in discussion with her rheumatologist. She did not mention that she had severe side effects like  male patient, but when she experienced a recurrence during the BCG treatment, she went ahead with surgery to remove the bladder.  

Autoimmune disease is when our immune system, namely killer T-cells attack healthy cells.   We do not know the reason why some people develop autoimmune diseases.  So, the treatment requires balancing of intentionally reducing the level of immune response so it lowers the symptoms of autoimmune disease but not too much so our immune system still respond to foreign pathogen such as BCG bacteria.   Because BCG treatment for bladder cancer depends upon our immune system responds sufficient enough to kill cancer cells,  we do not want to suppress immune response by taking immune suppressed  drug during the treatment also we know T-cells invoked by BCG not only kills cancer cells of bladder but also affect other organs in some cases such patients with RA. So, it must be managed very carefully.  Like Allan has suggested, your urologist and dermatologist if you are being treated for your psoriasis need to work together and come up with the game plan.

Alternatively, you may consider Gemcitabine + Docetaxel  (GEM-DOC) intravesical chemotherapy, which has established the treatment as alternative to BCG in various cases in many  academic  hospitals   In 2022, University of Iowa Team reported that GEM-DOC when it was administered to BCG naïve patients with high risk NMIBC (CIS and T1HG) , the recurrence free at  89%, 85% and 82% at 6, 12 and 24 months , which is better than BCG.   So, you may want to discuss this option with your urologist too.

pubmed.ncbi.nlm.nih.gov/35892270/