I do not know much about direct relation between the thickening of bladder wall and cancer. But, I read that most of the time, bladder wall thickening is caused by inflammation, which is the result of immune response. In this regard, though immune response is to kill pathogen or damages cells including cancer cells, I have noticed that recently more attentions are paid to the other affects of immune cells, that immune cells help cancer to grow. They say immune cells form a part of tumor micro environment (TME) in the connective tissue and the cancer cells recruits immune cells to help tumor grow. For example, immune check point PL-D1 protein which prevents T-cell to attack to kill cancer cell is often found in immune cells in addition to cancer cells. In this case, immune cells in TME are helping cancer cells evade our immune cells (T-cells) from their attacks. In this context, it is known that immunotherapy, e.g. Keytruda is more effective for those with higher number of PD-L1 protein, which bladder cancer cell secretes out of the cell and attach on the surface of the cancer cell. PD-L1 helps cancer cell evade our immune cell (T cell) from its attack. It turns out that immune cells which are recruited which supposed to help attack the cancer cell are found to have PD-L1 protein. So, when they check the eligibility of immune check point inhibitors such as Pembrolizumab (Keytruda) if it is going to work for the patient, the pathologist who checks the patient's cancer specimens must count PD-L1 on immune cells around cancer cells and PD-L1 on cancer cells. This may be an example, immune cells which cause inflammation, which also result in thickening of bladder lining (wall) help cancer growth. But, those studies on the internet generally assume that the cancer cell is because of multiple gene mutations, and one of mutated gene is recruiting immune responses to help the cancer cell grow. For example, a study which was published in Cell Journal in 2015 states that in mice, PTX3 deficiency unleashes tumor promoting inflammation. Tumors developed in a PTX3 deficient context have higher frequency of mutated Trp53. Trp53 is the mouse version of TP53, which were identified in mutated form in muscle invasive and HG / CIS non-muscle invasive bladder cancer.
In clinically though, yes, some chronic inflammation increases chance of cancer, eg. Helicobacter pylon bacteria caused infection for stomach cancer and Chrone's disease which is chronic inflammation of bowel increases chance of cancer, but the chance of developing bladder cancer seems to be low. For example. Interstitial cystitis (IC) which is chronic inflammation condition of bladder has been shown to increase bladder cancer. One study showed .32% of IC patients was diagnosed with bladder cancer and another study saw 6 out of 600 was diagnosed with bladder cancer during 3 years follow up. When we compare the probability of being diagnosed with bladder cancer is general population per 100,000, the demography of bladder cancer is as follows,, 0.2 0-19 yrs old, 1.1 20-39 yrs old, 17.1 40-59 yrs old 134 60-79 yrs old, 380 80+ yrs old according to one stats. If you are 65, the chance of having the bladder cancer is 150/100,000 or 0.15%. So, people with IC has twice more chance than general public to be diagnosed with bladder cancer according to the calculation. Still we are talking about .32% chance if the bladder thickening is caused by IC. Also, there are various effective treatment for bladder cancer especially in recent years if you happen to be one of 0.32% chance.
Incidentally, you may want to ask your urologist to have urine analysis such as cytology regularly as surveillance protocol to detect bladder cancer if and when a tumor shows up.
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